Re: virtual machine
VM is great because you eliminate the need and time loss to reboot, and can run diferent OS in the same time.
I prefer VM on Linux or FreeBSD and WinXP inside VM, with controlled/no internet access to Win. This way Windows runs securely inside *nix OS, though a bit slow.
*nix is a very stable and secure environment, and makes work more secure.
Xen is based on qemu? I used qemu standalone on Linux, it doesn't have full virtualization, but is fun to use.