Unless you need span mode or your (Intel) Mac lacks performance, I can safely recommend Windows 7 64bit (making use of all your RAM) and the latest iteration of BootCamp (at the time of writing 4.x for X's prior to 10.8.x and 5.x for 10.8.x onwards, read this for official blurbs). Please read on if you're new to BootCamp on your Mac. Running vvvv via BootCamp is preferable to VM solutions, due to general performance disadvantages and some VMs lacking support for certain vvvv functionalities. Probably many vvvv novices owning Macs never bothered running Windows on their Macs, although it's quite easy to do so: Apple's free (being part of the OS) BootCamp let's you run Windows OSes on almost all Intel based Macs.