If I were you, I would skip Vista. Windows 7 is just better in many ways. You can download the Windows 7 RC for free.
http://www.microsoft.com/windows/win.../download.aspx
And then "upgrade" to the final Windows 7 later. If your computer can handle Vista, then it can handle Windows 7 better. You could either dual-boot your current XP install with win7 or just do a clean install. Thats up to you. (also, they do have the 32-bit version of Win7)
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These walls fall down around me but I will stand
And though my body be burned away I will live