All Xen 2.0.* ebuilds have been dropped from Portage. Unfortunately Xen 3.0 doesn't support Linux 2.4 kernels and support for them isn't planned yet. So there's no way to run legacy distributions with Xen on Gentoo. Xen 2.0.7 in ~x86 would be great. If that's not possible, could someone point me to an archive of the ebuilds so that I can setup an overlay?
As the ChangeLog says, xen-2 ebuild has been removed since upstream no longer supports them. You can grab the ebuild from http://www.gentoo.org/cgi-bin/viewcvs.cgi/app-emulation/xen/ but we cannot support something that's unmaintained upstream.