The xenpv-win-64bit package contains an image with the para-virtualized drivers for 64bit windows guests on RHEL5 virtualization hosts. The drivers need to asynchronously be added to RHEL5 in the VT channels. They initially need to go to the VT Beta channels. After completion of the beta phase, they need to be added to the VT channels of Server and Desktop (MultiOS).
The drivers were available for 5.3 already: http://rhn.redhat.com/errata/RHEA-2009-0266.html