OEM Software - okay or not? Need CAD program for Mac!!!?

I'm planning on getting a new Mac Book Pro (switching from a Dell) and I'm going to need to get some a new CAD software program as well, I use AutoCAD 2005 now and I'm thinking about switching to Vectorworks. However, I would like to be able to save some $$. Is it okay to download OEM software because I may want to get both Vectorworks and AutoCAD. And I can't seem to get a clear answer!!! Also, is there anyway to transfer the AutoCAD on my Dell to the new PC (I don't have the original discs). Thank you to anyone who can solve my dilemna!!!