http://wskills.blogs...-and-virtual.html
A Software Assurance chit gets you up to 4 VMs with a desktop license, but all others need a license for each VM. Unless things have changed, YMMV, etc., etc.
As is usual with anything Windows, it's not straightforward. 7 apparently allows native and VM installs on the same PC, but each must be activated separately. I've just skimmed this thread which talks about differences between retail and OEM versions - it appears that users are able to get MS to give out the magic numbers for the VM install activation with an OEM version, but more evidence might be needed.
http://forums.macrum...read.php?t=827339
Nothing is easy, at least not if you want to be reasonably legal without giving MS more money than the least they'll accept...
Cheers,
Scott.