I'm installing the CTP of Vista on a Virtual PC to check it out, but the install is going to take a while, and I don't want VirtualPC to hog my CPU while I work (no dual core proc for me yet). I have plenty of RAM, so that's not an issue, so my CPU is the bottleneck in computer speed. I found a simple solution that allows me to continue to work while a Virtual PC is cranking away.
Set the thread priority of Virtual PC to "low". Windows will now allow anything else to run more often than Virtual PC (cpu timeslicing). If you've never adjusted thread priorities before, you can do this with Task Manager. Notice that my Commit charge is high, but I have 2GB of RAM, so I'm not worried. At the top, notice that I have a NAnt build running. I want NAnt to go fast, so it's normal priority. The only process I've changed is Virtual PC.
Note: I almost never change thread priorities, and I don't recommend doing so, but in this case, it serves a specific purpose.
Windows Vista is slowly installing in the background while I'm able to continue to work without being affected. Virtual PC is effectively only using idle CPU time.