I'm using Parallels 3.0 and have 3GB of memory installed on my Mac Pro. My Parallels XP VM is configured for 720MB, my Vista VM for 1GB. When I open both at the same time the available memory shown in Activity Monitor (Inactive + Free) goes down to less than 200MB. In addition to this, all four processor cores start working quite hard all the time, even if nothing is happening on the Mac or in either of the virtual machines. As a result, everything becomes quite sluggish. Will adding more memory (e.g. up to 5GB) improve the speed? Or is the processor load when you have two or more virtual machines open independent of the amount of memory available? I also notice that all four processor cores keep working at around 12-14% all the time (System + User) when Parallels 3 is running with just XP open on its own, even if nothing is happening in either XP or OS X, and this is definitely more idle load than I had under Parallels 2.x.