installing a new operating system is all well and good, but the whole point of computers are applications. you need to figure out all the applications you use then find the *nix based version of them. basics like web browsers and media players are covered by the o/s, but you'll want open office to replace m$ office as a start, and you'll need to look for linux supported charting program.
*nix and MAC are generally "better" than windows in terms of stability (vista is still a pile of **** with its driver issues) but its all about the applications and most development is done for windows platform. as it stands now, a patched XP SP2 is a nice, stable, functional operating system, there's really not much reason to move away from it for personal use.