Command line linux doesn't take much to run by itself, but it matters what you are going to do with command line. If you are going to compile something, it will bacically be like on a regular PC in that it will take the amount of processor it needs to get something done as fast as possible. I'm not sure if Parallels can be like VMware where you can give only one processor to the virtual machine. By the way, I'm guessing at the Parallels thing, but I used VirtualPC on the PPC Macs, which when running windows didn't even use full processor unless you were doing something intensive. And that needed to translate from x86 to PPC. So my guess is that its not that bad.