A few days ago, I had to install Windows XP as a guest OS on my Ubuntu Hardy machine as I needed to carry out some Visual Studio work. What I noticed was that my CPU usage went through the roof (constantly at 100%) even if the guest was completely idle. Result: My laptop was shutting down within a few minutes because the CPU was heating up and its temperature going beyond 75C. And finally came to know a simple solution from a friend, that immediately worked. The solution was to create a new dummy guest machine in VirtualBox, allocate minimal RAM to it (I gave 4MB) and just run it, don’t even need to add boot disk to it and to my surprise, the CPU usage came down to just 3-4% immediately. I’m not sure why this issue is happening and how the dummy machine solved it but atleast it is working for me now. If you have a similar issue, you can try out the same.