I believe it was a mistake to put the latest VitualBox (2.2.0) into Entropy as it is not, in my opinion, ready to use. My virtual XP hangs unless I disable the USB devices. (I found that was the problem by creating a new one that worked well until I enabled USB devices and it then froze at the same point as my original and then found that the original booted OK once I had disabled the USB devices.).
Just found a workaround for the USB problem on the Vbox pages. Add Null USB devices, boot the guest OS (in my case XP) then plug the usb devices in and enable them from "Devices" once the OS is running.
Self-righteousness is a loud din raised to drown the voice of guilt within us - Eric Hoffer
Don't believe what it says on the right - I am anything but sagely; More oniony!