Windows Vista has been on the market for nearly a month now, but enterprise users and industry experts agree that Microsoft's latest and greatest OS still isn't yet ready to replace XP.

The problem is not with the software itself -- by most accounts, Vista is technically solid -- but with myriad peripheral issues that Microsoft must work out to take the pain out of using Vista.

Take patching, for example. On Dec. 12, Microsoft released an Internet Explorer 7 fix that improved the performance of IE's phishing filter. The software had been bogged down by Web sites with a large number of frames, and users had been complaining.

Microsoft patched the problem for Windows XP and Server 2003 users, but not for Vista. That update will come after the consumer release of Vista hits the market some time in January, according to a spokeswoman for Microsoft's public relations agency. And although Microsoft is now issuing security patches for Vista, performance-related updates such as the phishing filter are being handled on a case-by-case basis, she said.

Microsoft won't say why it is holding off on some Vista patches even though the product is commercially available for business customers, but Russ Cooper, a senior information security analyst at Cybertrust, has a theory.

"I say Microsoft never intended anybody to run Vista prior to January," he said. "What works on Vista, beyond Office 2007?" he asked. "I'm going to Vista ... when my VPN supplier tells me that they have drivers that work, and when my anti-virus vendor tells me that they have non-beta versions that work."

Cooper brings up a good point: Application compatibility is another problem for Vista, and VPN (virtual private network) and anti-virus software are among the applications at the top of the list that users say must work before they will move to Vista. Right now, the most popular software in those categories, as well as other mainstream applications many business customers use, won't be available for Vista until after the consumer version of the operating system is released on Jan. 30, 2007.

Some of the applications that still aren't compatible with Vista include IBM Corp.'s Lotus Notes e-mail and collaboration suite; Cisco Systems Inc.'s and Check Point Software Technologies Ltd.'s VPN clients; Intuit Corp.'s accounting software QuickBooks 2006 and earlier versions; and anti-virus (AV) software from Trend Micro Inc.

Intuit even took time in mid-December to warn QuickBooks users in a note that they should hold off on upgrading to Vista until after the U.S. tax season ends in April, citing compatibility with older versions of its software and "potential reliability issues" with Vista.

IBM said Lotus Notes will support Vista by mid-2007; Lotus Notes 8, the next version of the suite, also will be available at that time on Vista. Cisco's VPN will support Vista some time in the first quarter of 2007.

QuickBooks, Check Point's VPN client and Symantec and Trend Micro's AV software will support Vista following the consumer release. However, in some good news for users, McAfee Inc. already has Vista AV software on the market.

Even some of Microsoft's own products still don't run on Vista. SQL Server 2005, the latest version of Microsoft's database, won't be available for Vista until after the consumer release.

Still, while there may be some lag time in Vista adoption as users wait for applications to catch up to the new OS, companies will eventually have to make the switch to Vista no matter how painful it is. Most analysts predict that enterprises will begin moving over to Vista in earnest by 2008.

"Once Vista is being shipped by OEMs on all new PCs, we won’t be debating why people should move," said Andrew Brust, chief of new technology with consulting firm TwentySix New York. "It will be clear that they will need to do so, sooner or later. And honestly, people can argue until they’re blue in the face about how XP is fine, but the reality is that it’s five years old, technology has changed and a new OS is necessary."