Shares of Sun ( SUNW) vaulted an impressive 8.8% in Monday trading, tacking on 34 cents to $4.21.

The stock of the troubled company has now soared 29% since commencing its run-up on May 2, when it gained 12.3% in just one day. Shares have traded in a higher range ever since then.

The recent run-up has fueled rumors about a potential takeover of Sun, because the rising stock price can't be explained by any improvement in the company's core business. In its most recent quarter, Sun revenue tumbled 10% from year-ago levels.

Yet analysts generally pour cold water on specific takeover theories. "Sun's business continues to implode. The takeover rumors... when I finish laughing, I always ask who," says one buyside analyst reached by phone today. "The most common one I hear is IBM ( IBM), which doesn't make a lot of sense." The two companies sell competing lines of Unix-based servers.

Another rumored buyer, Dell ( DELL), makes even less sense given their sharply differing strategies, says the analyst. Dell, which positions itself as a low-cost standards-based vendor, spent a mere 1.2% of revenues on R&D last year, while Sun, which touts its high-performance technology, spent 14.6%. "There's not a chance that Dell would want Sun. Their mindsets are completely opposite," says the analyst.

In related news today, buyout firm Silver Lake Partners tapped ex-Sun president Ed Zanders as a managing director, according to a Reuters report. Zanders left Sun last summer along with a handful of other high-level execs.

The development means Sun would have a high-level contact if it wanted to pursue a buyout or other deal, but the buyside analyst said such a deal is highly unlikely. "I think you'd have to have CEO Scott McNealy removed before anything like that could happen. And after talking to him for many years I just don't see it. He's got a lot of shares and a pretty packed board."

According to a proxy filed last September, McNealy owns about 2% of Sun's outstanding shares, or 56 million shares, with the right to acquire another 16.4 million.

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