Have a look at the user guide (section 3.1.2 in my copy). I had some problems in the past with 64-bit guests on 32-bit Vista, but that laptop died and I now run Win7 Ultimate, so I don't face the problem anymore.
And Arch runs just fine as a guest BTW.
Last edited by syg00; 09-27-2010 at 10:36 PM.
Reason: added section reference