I think you might be a little confused there. Fusion can use up as much CPU resources as your computer has. There is very little overhead. The big difference would be in playing games where you'd need full 3D acceleration. In that case, Boot Camp would be the better option.
More information here.
hm... the virtual machine runs slower the higher you set it or your macintosh runs slower? what kind of apps are you running in windows?
i have VMware fusion but when i run it, i don't think much of my cpu power is running with it. is that true? if so, would me running windows via bootcamp allow me to use full cpu power for windows?
When I had parallels, which is very similar to VMWware, it didn't allow me to choose how much memory I'd like to use; the default was 512 MB. Oh yeah, and I have 2 GB of Memory like you do, going to update to 4 when I get to New York though ^^.