Reply: Parallels or VMWare
I've tried both Parallels and VMWare Fusion and It's really a user choice, but I do like that VMWare allows you to go out to it's library and download other OS's to try out under VMWare like Kubuntu, Red Hat, etc...Again personal choice. I currently have A Macbook Pro 15.4" Running OS X Leopard, Windows XP (Bootcamp), Windows XP (VMWare Image, Ubuntu 8.0.4 VMWare image) I love it. I do recommend getting 4gb of memory if you want to really do it up right.
;P