One thing he missed in dicussing using on a Virtual Machine however is that provided your CPU has VT enabled in the Bios or by default you can actually run the X-64 version as a guest OS on a 32 Bit host such as XP. Note if you do this however the HOST machine will still only see 4GB RAM max so your guest OS will have to use less.
You can also get the interesting scenario of running Windows 7 x-86 as Host with x-64 as a GUEST -- but subject to the same constraints.
Execute the attached file to see if your CPU will support a 64 bit Guest OS. Note Virtual pc doesn't support 64 bit guest OS'es so you'll have to use something like vmware.