Responsiveness -- VirtualBox

I’ve never really run into this problem since I left Windows. I am doing some software testing so I need to run windows and I do so inside VirtualBox. I have a core2duo 2.4 GHZ and 2GB or memory and I give WinXp 512. When I’ve got it running and I try and use other apps the mouse kind of sticks or doesn’t respond. I tried renice to give VirtualBox a lower priority to 10, but it didn’t really help.
I see that I can change the kernel scheduler, I’m really only familiar with CFS, which one is best? One of the things I’ve always loved about linux is that even under heavy load while encoding video or stressful stuff the system still responds fairly well.

Nevermind, I set it to CFS and it’s all good now. Why isn’t CFS the default? What is the default?