VMware users note you CAN run a 64 bit Guest from XP
to those of you still running XP you CAN run Windows 7 X64 as a guest (assuming you have the Virtualisation feature enabled) or even if you have Windows 7 X86 you can still test the Windows 7 X64 system out.
This is a good way to try out to see if you like the X64 bit version and whether your applications will run.
Note that DIRECT hardware access applications such as DVD playing and some moderrn games won't work on a VM but nearly everything else should run just fine.
I mention this only because people are under the mistaken impression that you have to be running a 64 bit HOST in order to run a 64 bit Guest OS --not true.
The only limitation is that as the HOST 32 bit system can't see more than 4GB memory the number and size of your 64 bit GUEST OS'es will be limited.
This is actually a great way of testing out for example the 64 bit version of Office 2010 even if you are on XP.
You'll need vmware workstation or vbox installed on the host but it will work just fine (including the AERO effects on Windows 7).
System Manufacturer/Model Number Custom built OS W7 X-64 RTM,SUSE 11.1, XP PRO SP3 as a VM, VMware ESXi CPU Q9400 QUAD Motherboard P5QL-CM Memory 8GB Graphics Card On Motherborad Sound Card Realtek HD audio Monitor(s) Displays Apple Cinema display
Mouse Toshiba wireless laser Hard Drives 4 X 1TB SATA Internet Speed > 20MB up
Just a little addition in case you are not allowed (or able) to install virtualization software on the host. If so, then you can boot into winpe (like bartpe etc) and run vmware (player or workstation) from there. Then you can test 64-bit vm's without touching the host OS.