I was planning on holding off on Vista / XP 64 until there's a few more applications that state that they are happy on that platform. I would not expect C5 to benifit from that OS just yet as it's still a 32bit application.

You might want to consider spending money on another GB ram before you upgrade. I saw an article in Custom PC that said that some resource hungry games needed 2GB in Vista when they were ok in XP.

I've actually got just upgraded to that same hardware platform, just with cheapy motherboard graphics... Not actually installed C5 yet!