If you want to start experiencing 64bit computing, get the Windows 7 64bit. Free, lightyears better than Vista.. and can go along with 32bit xp.
Ive had Windows 7 64 as my only os for quite while now.. i play GTL, rCraptor, GTR2, iRacing, LFS, GTR Evo, FSX, FS9, Rise Of Flight, IL2, Ship Simulator etc.. anything
without problems, and with great performance too. Most companies are allready releasing official drivers for Windows 7, for example ATI just did a week or so ago.
I can very strongly recommend.. Im still stunned how good and trouble free this bloody os is..