Ubuntu in a VM on OS X?

I’m trying to get Ubuntu 10.10 running in a VM on my iMac. It mostly works with either VirtualBox or VMWare Fusion, but I can’t get 3D acceleration working. Under VirtualBox, I can get compositing happening, but it’s very slow. Under VMWare Fusion, Ubuntu won’t even acknowledge that I have a 3D card. Help.

Edit: If you can point me to a working guide for dual booting Ubuntu on the iMac 27", then that would also be great.