Well, the fact you've been given an AutoCad for Mac licence basically answers your own question doesn't it?
You could:
1) Stick with ACad and with your limited funds upgrade your PC
2) Sell the ACad licence and upgrade your VW 2008 to 2012 (you have missed out on a lot of VW's recent development if you currently use 2008)
3) Go back to hand drawing
I have formed the view, that if you run CAD on a mac, you inherently give up some of the ability to collaborate effectively with other consultants in the windows world.
If you are a mac guy, you only really have two options - Archicad and Vectorworks. (I haven't included Autocad for Mac because in it's present form it is a general cad app and not aligned towards architecture, from what I understand i.e. Autocad Architecture not available on mac)
Archicad's interface for mac is appalling, although a closer competitor to Revit than VW.
If Revit came out in a mac version then it would be goodnight nurse for VW.
BTW, I've used Autocad and I never have liked it.
Download VW 2012 and try it out.