STOCKS TO WATCH: Apple, Compaq, Net Perceptions and Research In Motion

The run of good fortune finally came to an end for Apple Thursday when it warned that its fourth-quarter sales and earnings will miss analysts' estimates.

Company officials said it will report sales of between $1.85 billion to $1.9 billion, just slightly better than $1.83 billion it recorded in what most analysts considered a disappointing third quarter.

It now expects earning to fall between 30 cents to 33 cents a share in the quarter, well below the First Call Corp. consensus estimate of 45 cents a share.

Apple blamed slow sales of its Power Mac G4 cube PCs as well as sluggish sales in all geographies and in its education business.

Its shares closed up 4.56 to 53.50 ahead of the warning. The stock fell to 42 in after-hours trading but rallied back up to 52 within a few minutes.

"We've clearly hit a speedbump, which will result in our earning, before investment gains, approximately $110 million rather than the expected $165 million for the September quarter," said CEO Steve Jobs in a prepared release. "Though this slowdown is disappointing, we have so many wonderful new products and programs in the pipeline - including Mac OS X early next year - and remain positive about our future."

Sanford Bernstein analyst Vadim Zlotnikov said he wouldn't characterize the fourth-quarter profit warning as a "speedbump," pointing out that Apple's recently battled through two or three major upgrade cycles for its popular powerbook and iMac machines.

"Overall consumer demand doesn't appear to be as low as Apple's numbers indicate," Zlotnikov said. "It looks like sales of its G4 cubes haven't taken off they way they expected. At least so far."

Compaq will be worth paying attention to on Friday after it announced that Chairman Benjamin Rosen was retiring after 18 years with the PC maker.

Chief executive officer Michael Capellas will now serve as the company's chairman.

Its shares closed up 1.65 to 30.80 Thursday.

"Michael's appointment is a natural and appropriate step for Compaq at this moment in our history," Rosen said in a prepared release. "After almost two decades as Chairman of the Board, I have complete confidence in Michael to lead Compaq during the next great phase of the company's growth and global expansion."

Rosen was a founding member in 1982 and appointed chairman in 1983.

In its latest quarter, Compaq met analysts' estimates, earning $387 million, or 21 cents a share, on sales of $10.1 billion.

First Call Corp. consensus is for a 29 cents a share profit in its third quarter and $1.08 a share in the fiscal year.

Net Perceptions will be active Friday, probably to the downside, after warning that it will miss analysts' estimates this quarter.

The maker of online personalization and merchandising technology said it expects to report a loss between 22 cents to 32 cents a share in the quarter.

Analysts were expecting a loss of 13 cents a share.

Its shares fell to 8.74 in after the bell after closing off 0.38 to 12.50 in regular trading.

It now expects sales between $6 million to $9 million in the quarter.

"We are committed to aggressively addressing the new realities of the marketplace in order to get our business plan back on track," said Steven Snyder, president and CEO, in a prepared release.

Research In Motion beat the Street in its second quarter but still lost $1.6 million, or 2 cents a share.

Analysts were expecting it to lose 3 cents a share in the quarter.

The stock closed off 1.59 to 83.44 ahead of the earnings report, before jumping to 87 in after-hours trading.