And now? More than two years after its launch Vista has managed a penetration of just 9 percent, according to a released last week, giving it the dubious distinction of being the least popular new Windows OS out of the gate, ever.

But things are looking up for Vista. This year finally will be the big one, says Forrester. Really. Thirty-one percent of the 962 North American and European IT decision makers interviewed for the report have already begun migrating to Vista; another 26 percent plan to start in 2009 or later.

On the other hand, "IT decision makers don't have an entirely rosy outlook for Windows Vista," wrote analyst Benjamin Gray. Some 28 percent of respondents have not yet decided about whether or not to migrate, and 15 percent plan on skipping Vista altogether and going straight to Windows 7 when a final version is released in 2010.

Here's how enterprises currently break out, according to the report: 71 percent still use Windows XP, 10 percent use Windows 2000, 9 percent use Vista, Apple's Mac OS X and "other" each garner 3 percent, and 2 percent use Linux.