Be warned for anyone interested in running 32bit guests on 64bit dom0 instances that it us currently not supported in CentOS 5.1. This will apparently be corrected in the upcoming release of RHEL (5.2) which is scheduled to make it's appearance in a month or so. (It should have left beta May 7th).

The stability is SO bad that the image won't even stay up for a single day. You have been warned. Stay away from mixing 32 and 64 bit OS's. Note that this has long been fixed in the Xen repos. One would just have to figure out how to go about building Xen by himself. Not suggested for production environments either..