Ask Max: Optimal RAM For Running Virtual PC
How much RAM is optimal for running Microsoft Virtual PC (7.03) on a DP 2 GHz Power PC G5?
Even though the Intel switch has changed the efficiency of virtualizing a PC on the Mac, virtualization's RAM needs have remained the same. Just like using Parallels or VMware, Virtual PC needs a ton of RAM. The truth is that you can never have too much RAM for increasing the performance of a virtual machine. However, a general guideline would be double the RAM you would want in any one of the operating systems you are running. If your Power Mac runs well by itself with 2GB of RAM, look at taking it up to 4GB to comfortably run the Windows OS next to the Mac OS.
You can use less, but in general that will get you to the optimal position. Use no less than 1GB of RAM to run a Virtualized system on your Mac.