All of this spells trouble for Microsoft, which last week forecast an 8-10 percent increase in Windows unit sales through June 2007. At the meeting last week, Microsoft executives repeatedly stressed how important Vista will be to the company's 2007 revenue picture.

"Vista could be very far on the horizon for most companies," said Wilcox. "It's even possible that if enough businesses are dissatisfied with Vista, that volume license contracts might increase so that customers can exercise downgrade rights and put XP on their systems."

JupiterResearch's survey showed that a majority of enterprise systems currently use Windows XP, although Windows 2000, and to a lesser extent, Windows NT 4.0, still remain prominent in business. Vista may not be able to dislodge those operating systems quickly.

Part of the hesitancy is because of the constantly-shifting messages businesses have received from Microsoft.

In late 2004, for instance, Microsoft was adamant that Vista would be widely available during 2006. Companies which took Microsoft at its word and developed plans for deploying the OS have had to make changes.

"Each time Vista's delayed, Microsoft loses more credibility with businesses that have come up with deployment plans," said Wilcox.