TC 4.0 was the first to use 3.0.3 kernel, and all those libs and such should pretty much be up-to-date. In theory, you just need to get that compiletc (not sure if that's the right name?) extension and compile the Xen source. Haven't messed with this stuff for a while now though, so I'm not sure if it'll really go that smoothly.
Sorry for grave digging, but I figure this topic is on the first page of the subforum anyways.