I don't know if people have mentioned this before, for people who has a power development computer, Virtual PC is the way to go.
Virtual PC 2007 from Microsoft is a free download. Or you can get one from VMware or other companies.
I have setup my Virtual PCs that each with different version of the IE (and other goodies such as Microsoft Java and Sun Java, and different Flash versions) Each Virtual PCs takes about 2 GB of HD space.