If you're a hyperactive trader, then you know that nothing beats the professional-level market-watching software from brokers like Tradecast.com, CyBerCorp.com or from financial data providers like eSignal and WindowOnWallStreet.com. To get a sense of how much market information these systems hurl at your cerebrum, try out the demos on their sites. What you'll see are multiwindowed platforms that provide constantly updating quotes, charts and news.

Of course, you'll pay for all the bells and whistles these professional systems provide. For example, the minimum price for Level II quote data (I'll explain what that is below) is $50 per month, which covers the exchange fees charged by

Nasdaq

. Usually, brokers waive these fees if you make a minimum number of trades per month. However, if you sign with an independent data provider like WindowOnWallStreet.com and brokerage services aren't part of the deal, expect to pay the $50, plus an additional $80 per month for use of the software.

If you're a serious trader, you'll happily pay for a reliable system like those mentioned above. But if you're just getting started or if you just want to have fun watching the markets, save your money. By registering with a handful of free sites on the Web and then viewing those sites via several windows on your screen, you can create something pretty close to professional-level trading software. In some cases, the free applications are better than the stuff you pay for.

Let's start with

Money.net, which offers a java app called the

Screamer

. Using the Screamer, you first create a portfolio of stocks that you own or want to watch. When you're finished, you can watch your positions update in real time, right before your eyes. In trader's parlance, this is called streaming, real-time quotes. (Alternately, it's called a Nasdaq Level I screen.) By watching prices change, you get a sense of the stock's momentum.

Now suppose XYZ Co. catches your eye. If you want more information on how that stock is trading, open up another window of your browser and log onto

freerealtime.com. This site offers real-time snapshot quotes, which means you have to hit the refresh button on your browser each time you want to view fresh data. In addition to the size of the bid and ask, freerealtime.com shows you the size of the latest order, plus the last four ticks. This information often can tell you whether the stock is trending or drifting and if those traders making orders are individuals who might buy lots of 1,000 shares or less or institutional traders who might place 5,000- or 10,000-share orders.

Obviously, a large order is going to affect the supply and demand for a stock in the short term. However, it would be nice to know if these large buy-and-sell orders were isolated or part of a pattern. And that's what

Thompson I-Watch tells you. As the name implies, I-Watch monitors institutional activity. Enter a ticker symbol and you get a graph that neatly shows what large buy and sell orders have been placed during the course of the trading day. Buy orders appear in blue, sell orders in red. The color-coding lets you see at a glance where the pressure's coming from, plus whether institutions or individuals are dominating the trading over a period of time. The information is updated every five minutes.

Professional trading software usually comes with charting packages that update in real time. What's more, these charts let you overlay technical indicators such as a moving-average line or a trend line. Many daytraders live and die by these charting tools, using them to time second-by-second entry and exit points.

So far, there is no comparable real-time technical charting available for free on the Web. But if you're a swing trader who holds stocks for several days at a time, you might try

MetaStock Online. This

Reuters

(RTRSY)

-owned site is basically a demo for a more sophisticated charting package that costs $400. MetaStock's intraday charts use 20-minute delayed quotes. And you can overlay any of 21 technical indicators.

As detailed as all this information is, it still doesn't compare with what you can discern by using a Level II screen. How come? A Level II screen not only gives you the real-time price of a stock, it shows all the orders that are off the price by a fraction or so. And just as important, it shows you where those orders are coming from, whether they're from a market-making firm such as

Knight/Trimark

(NITE)

or

Merrill Lynch

(MER)

or from an electronic-communications network, or ECN, such as

Island

. Die-hard daytraders grow adept at watching Level II screens.

Over time, some get to know how market makers for the stocks they trade tend to behave. Is the market maker trying to lure in sellers with a tasty buy offer only to withdraw it moments later, substituting a lower offer? Is he buying to cover his own short position? Such dramas enacted daily between market makers and daytraders can be more addictive than hanging out at

eBay

(EBAY) - Get Report

Nobody's giving away Level II information on the Web, yet. But there's a pretty close approximation that is free. And you'll find it at

Island.com. Island, as you probably know, is an ECN that directly matches the trades of buyers and sellers. By clicking on what's called an order book you can view all the buy and sell orders for a stock, arranged by price, and constantly updated, just as with a Level II screen.

There are two important differences between the Island order book and a Level II screen, however. First, the Island order book only displays trades made on Island. That said, Island handles an astonishing 12% of all Nasdaq trades. So prices on Island are fairly reflective of the overall market, though there may be a better bid or ask price elsewhere at any given time. The other important difference between the Island book and a Level II screen is that all Island orders are anonymous. You don't see who's placing the order -- just the size and the price.

Island has a link to another site with a real killer app that's not available on professional order-execution systems:

3D Stock Charts. By registering, you can pull up the Island order book and also a chart with red and blue lines depicting the total numbers of buy and sell orders in real time. As with Money.net's streaming real-time quotes, 3D Stock Charts' java app updates before your eyes. You see at a glance whether buyers or sellers are dominating at any given moment. By watching the sea of red change to a sea of blue, you can deduce whether diminishing supply will result in a near-term upward movement in price.

This data is only a visual representation of the backed-up orders in the Island book, but again, it's probably reflective of the order flow taking place in the market as a whole. To find out, watch the action on 3D charts in one window while watching the streaming quotes on Money.net in another.

Before you try any of this at home, be aware that since you're watching two or more different Web sites at once, there'll probably be a time difference in how each sends information to your screen. This time difference could show up as a fractional difference in a stock's price, especially with high-volume stocks. Also, putting a lot of java apps up on your screen at once can cause your computer to crash, not something you want if you're trying to get out of a stock, quickly. So test out the various windows thoroughly before you log onto your broker and start trading.

Mark Ingebretsen is editor-at-large with

Online Investor magazine. He has written for a wide variety of business and financial publications. Currently he holds no positions in the stocks of companies mentioned in this column. While Ingebretsen cannot provide investment advice or recommendations, he welcomes your feedback at

mingebretsen@onlineinvestor.com.