Yesterday I tried
VirtualBox on my Mac. It is an Open Source virtual machine made by Sun. You can use it to create a virtual Windows machine on your Mac. In some respects it's even better than
Parallels which costs US$ 80.- For instance, it ran 64 bit Windows 7 beta with no problems at all, while Parallels 3.6 can't handle 64 bit OS's (I don't know about Parallels 4.0 because I don't want to pay 80 dollars again for Parallels). I guess you will be disappointed if you try to run applications that rely heavily on DirectX, but for most office work it seems perfect.