http://www.microsoft.com/windows/windows-vista/quick-start/service-packs.aspx

I have been working with SP2 for a while and have noticed that my system runs a whole lot smother.
They have come a long ways. I still love windows vista but I love windows 7 more. This release is a
must have. Download windows vista sp2 through windows update. For best results I would recommend
a fresh install of windows vista then do all of the system updates. There just nothing like a clean install.

Remember to backup all of your documents and files that are important to you before doing any
major update to your system.