A note by Johnny Hughes in http://bugs.centos.org/view.php?id=2189 (comment 6644):
"As a side note ... if the clock GAINS (runs to fast) time you should be able to fix it with this:
(by setting the correct host.cpukHz) and vmware tools should adjust a clock that is too slow.
Also see this blog entry concerning host.cpukHz:
http://blog.autoedification.com/2006/11/vmware-guest-clock-runs-fast.html "
Taking the advice from a few people and web pages, I made this change to grub.conf:
kernel /xen.gz-2.6.18-53.1.4.el5 divider=10 clock=pit
The clock is better but still not fixed. It jumps forward less often.
Jack