Shares of Rackable Systems ( RACK) plunged in late trading Thursday after the company beat second-quarter expectations but guided lower for the current quarter.The stock was recently off $10.19, or 29.2%, to $24.72 on Instinet. The server and storage product maker said net income for the second quarter rose to $5.3 million, or 18 cents a share, from $1.2 million, or 7 cents a share, a year earlier. Excluding items, Rackable earned $8.1 million or 28 cents a share, beating the Thomson First Call survey estimate of 28 cents a share. Revenue rose 5% to $88.6 million, beating First Call's estimate of $84.3 million. But the good news ended there: Briefing.com reported that the company said in its conference call that it expects to post third-quarter revenue of $80 to $85 million, below First Call's projection of $84.3 million. For the full year, Rackable expects revenue of $345 million to $355 million, according to Briefing. First Call was expecting revenue of $345.1 million.