It should work, since the commercial version works with Windows 7.
I think you should get Vista with the option to upgrade to Windows 7 (which most manufacturers are selling now). That way, by the time you upgrade, Solidworks will probably have support for Win 7. That assumes you are buying from a manufacturer. If you are building your own, just go with Win 7 release candidate.
I would get 4 GB ram and 64 bit operating system. There aren't really any disadvantages to 64 bit OS nowadays.
The current version of student editon 2009-2010 is not supported on Windows 7.
Chris suggestion can be followed regarding the RAM and OS recommendation for x64.