Gartner has issued a "clarification" to its recent advice on Windows Vista upgrades, pointing out that, after all, it doesn't think companies should ignore the operating system until 2008.

Earlier this month Gartner published a research note on Vista, called "Ten reasons you should and shouldn't care about Microsoft's Windows Vista client", which was generally lukewarm, noting that it will mainly offer "incremental, evolutionary improvements" over predecessors like Windows XP and Windows 2000. Most companies could safely hold off upgrades until 2008, Gartner said at the time.

It seems the research firm felt this ambivalent attitude was being interpreted in the wrong way, however, and this week published a second research note giving stronger reasons for upgrading - especially for Windows 2000 systems.

Upgrading in 2008 in fact means companies should begin testing Vista as soon as it comes out next year, since preparing for migration takes around 18 months, Gartner said in the new statement.

For Windows 2000 installations, of which there are a substantial amount, the situation is more urgent. Newer versions of some applications aren't supporting Windows 2000, and moreover, Microsoft's extended support for the system will come to an end in mid-2010. Windows 2000 systems will need to be replaced all-out, unlike Windows XP systems, which can be migrated gradually, Gartner said.

The new remarks reinforce comments made last week by Michael Silver, research vice president and co-author of the earlier report. "If you’re on Windows XP, you have more runway because you’re on an OS that is not only supported by Microsoft but also all the applications vendors," Silver said. With Windows 2000, however, support from other software vendors has already "started to wane", he said.

Gartner said it still stands by its original advice on Vista, and is only clarifying it.