I've heard of people doing this before. It's been a couple of years but the process involved going from LV 2 to 3 on the MAC. Then from 3 MAC to 3 LV. Then use the LabVIEW converion kit. You may be able to bypass the 2 to 3 on MAC step.
From my understanding you can open LV 4 and onwards VIs with LV 6. Here's a Knowledgebase entry you might find useful:
http://digital.ni.com/public.nsf/websearch/6f80a168949d5799862569310076f14b?OpenDocument
Another KB entry discusses how to move files between the PC and MAC:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/5b64515b3246bd8b862565210079a8dd?OpenDocument
Best of luck,
Kamran