The Xen 3.0.4 guest RPMs are pre-built RPM packages for particular 
enterprise linux distributions. Unlike the standard 3.0.4 host RPMS, 
these do not include Xen itself or the tools, but instead just include
a kernel suitable for running within an unprivileged guest ("domU"). 

Each of the guest RPMs is tailored for a particular enterprise 
linux distribution; in particular, the kernel is a patched version
of the standard kernel which ships with that distribution. Hence
for RHEL 3, we have a guest kernel based on linux 2.4.21; for SLES 9, 
one based on linux 2.6.5; and for RHEL 4, one based on linux 2.6.9. 

Note that these kernels are provided by XenSource, and are not 
officially recognized or supported by either Red Hat or Novell.