I bought VMWare workstation for Linux. Running dual-head X with a huge VMWare window (just smaller than my real size) on the right head, running Win2k Pro. And to my left (tibook, "3rd head") I have OS X. Browser testing? No prob.
If this isn't the coolest thing ever, I don't know what is.
So integrated, fast, and easy to use. I'm incredibly impressed. And the install process was so intelligent, even though I wasn't running one of the common Linux distros... it built kernel modules for me! And it all works on my desktop, which has no physical disks (root on NFS).
$300 is a bargain!
Now, time to install some more guest OSes... need Win95 and 98, if I can find those CDs back.