in MY OPINION (just thought i would state that as im not an expert etc)... if you are running Vista, downgrade back to XP with SP3... Vista uses up like 2-3 times the amount of resources of its extra security features and other more pointless things like the Sidebar... better yet, wait for Windows 7 to come out... ive beta tested it and so far it seem good... its XP but with the Vista look (as in its not heavy on resources but looks more modernised)
jm2c
Part right, part wrong. XP now really should be junked. Its 8yrs old (and that is an awful long time in software).
Vista is an excellent OS. By default, it is heavy on some resources, particularly memory. Turn off the Aero, and get rid of the sidebar, and it becomes less resource intensive (still more than XP). Do not be tempted to turn of UAC like many magazines and other uninformed 'specialists' tell you - it adds a vitally important layer to security that was always missing from NT based Windows (non NT based Windows never had security

), seeing as everyone seems to think they always need to run as Administrator, else its a smear on their penile performance.
Windows 7 is nothing like XP, thank god. Windows 7 is most definately Vista, just the next evolution. Certainly the betas have shown that the Out-of-box defaults are better tuned, and Microsoft have put a lot of work into startup speed - the big killer with Vista.