First tried to install Xen on FC6, but the initrd always failed for my machine, probably because of the changes made by previous stk16 kernel used for wireless support. It worked only after installing FC6 from the start. When the kernel was updated to kernel-xen-2.6.20-1.2948, the virtual manager complained not to be able to connect to the server.
Qemu seems developed specifically for Debian. VirtualBox also not easy to install for Fedora. Xen is very easy to install for Fedora.
Then tried VirtualBox under WinXP. Since my hardware was pretty old, everything would just be working a bit hard for more than one guest OS if possible. How about VMware? I don’t know.
Based on my system, I just gave up the potential to virtualization.