I've grabbed it from MSDN and am using it now. Couple of things to be aware of:
1. You can't install the 64bit version if you have any 32bit Office apps installed. I uninstalled Office 2007, tried again, and it still complained because I had Visio 2007 installed. Had to remove that as well before it would install. I guess this means that I will need the 64bit versions of those apps when I come to reinstall them.
2. The 64bit version of Outlook is not compatible with the CRM 4 plugin. Apparently the 32bit version is though.
I haven't tried to install the 32bit version of 2010 over a 2007 install, but I'd guess it would be a smoother experience than moving to the 64bit version.