Updated from 2:43 p.m. EST with new stock prices

Small-cap stocks jumped early Thursday morning then waffled around the baseline as the broader market undulated in positive territory.

Plexus ( PLXS), a Neenah, Wis., provider of electronic manufacturing services, shot up 11.9% to $22.20 after announcing fiscal first-quarter earnings after Wednesday's close. Plexus' earnings, at $27.3 million, or 58 cents a share, fell short of the Street's expectation of 60 cents a share. However, the company guided for second-quarter EPS between 46 and 51 cents, ahead of the average analyst expectation of 42 cents a share, per Thomson Financial. Plexus is a component of the S&P SmallCap 600, which was gaining 0.1% at 362.44.

Meanwhile, Edmond, Okla.-based Bronco Drilling ( BRNC) saw shares lift 16.6% to $15.64 on news that Allis-Chalmers ( ALY) would buy the oil and natural gas driller for $437.8 million in cash and stock. Shares of Allis-Chalmers were also rising, 4.8% to $11.32.

Print and visual communication services provider Cenveo ( CVO) also got a boost after reaffirming guidance yesterday after the close. For full-year 2007, Cenveo expects $300 million in adjusted earnings before interest, taxes, depreciation and amortization. Wall Street is looking for the Stamford, Conn., company to produce EBITDA of $248.5 million. Cenveo shares were up 21.9% at $15.55.

On the losing side, bond insurer Security Capital Assurance ( SCA) dropped 30.61% to $2.63 after Fitch Ratings stripped the Hamilton, Bermuda, company of its triple-A rating last night. Fitch downgraded the company to an A rating after SCA announced it would not try to raise new capital given the uncertainty of the bond insurance industry. Fitch's triple-A rating is necessary for SCA to conduct new business.

Also hurting was Flotek Industries ( FTK). The Houston oil, gas and mining services company lowered EPS guidance for 2007 to between 88 cents and 92 cents, down from a previous forecast for a dollar a share. Analysts polled by Thomson Financial predict EPS of $1.02. Shares sank 29.9% to $17.86.

More broadly, the Russell 2000 was up 0.1% at 692.69.