I'm new to Mac, too!
What Windows are you running, XP or Vista? And, what do you want to try to run through VMware? The gist of what I've read is that, if you want to run a demanding Windows application (like a graphics intensive game, CAD, etc.) you won't get the performance in a virtual machine that you would by booting into Windows natively, via Boot Camp; no matter how much memory you allocate to the virtual machine.
As far as allocating RAM for Vista vs. XP, most of what I've seen says to allocate 2GB if Vista and 1 GB for XP (what I am using). So far, so good but, I must confess, most of the time we have been running XP natively because my wife has been working on a project using some programs that run under Windows, and she is reluctant to try using the VM in the middle.