I just got vista x64 Home premium and I have XP pro x86 installed. I have no way of backing up my data but I do have my game saves saved to a flash drive.

Would it be ok to just do an upgrade install? My computer has no infections currently and runs well, I am just wondering if doing an upgrade will screw everything up.

So I guess my question is can I do a upgrade without my system slowing to a halt or do I need to do a clean install for good results?

I guess I should also mention I have nothing but game saves worth backing up, eveything would just need to be reinstalled, ie. my games and mods (which I also backed up).

The general rule embraced by most any expert/enthusiast you will ask is to always do a clean install unless there is some pressing reason not to. Historically in place upgrades have been problematic. It might work fine, but then again it might not.

I'm not sure if there are any new guidelines or statistics on this question but if it were my system I'd do it clean on general principles. A little more work but you're using it over the long haul and you'll be glad later you did. That you are going from 32 to 64 only complicates the issue even more. Some apps will need 64 bit versions to even run. Not many but some key apps often do, such as some anti-virus programs and emulation programs like Daemon tools.

In your case, you cannot upgrade from x32 to x64. Not supported. You will be forced to reinstall. You can try it if you want and you will see during the installation that the "Upgrade" will be disabled, then you can cancel the installation.

http://www.microsoft.com/windows/p [...] paths.mspx

My recommendation are always:
1) Unplug your current HD.
2) Install a new HD and Install Vista on it.
3) Replug your old HD.
4) Reinstall your app and transfer your data from your old HD.
5) Use BIOS Boot Manager to switch from XP or Vista.

This way you:
1) Can reboot to XP using BIOS.
2) Vista doesn't work well or hate it, return to old HD.
3) Don't loose files in case you forgot one.

I have Vista x64 and 4GB and happy with that. Just sad that I have 4 * 1GB and would like to go 8GB one day but no hurry for now.