Hi,
There don't appear to be any Windows x64 drivers for the Catweasel, and there also don't appear to have been any announcements saying there will ever be any, which is a bit unfortunate.
I guess you could dual-boot your existing machine - and XP drivers for your existing hardware should be easy to find.
I've intentionally kept an x86 XP machine for this purpose, and for other hardware that I can't use under either Vista x64 or Ubuntu x64...
- Ali