Been having some weird problems on a debian guest running on VMware server. The clock was losing about 12-13 seconds every minute. After some research we found some kernel options that drastically reduced the drift to such an extent that we can use an hourly ntpdate command to keep the clock in sync.
We edited the /boot/grub/menu.lst file and modified the "kernel" line from this:
kernel /boot/vmlinuz-2.6.18-4-686 root=/dev/sda1 ro
kernel /boot/vmlinuz-2.6.18-4-686 root=/dev/sda1 ro nosmp noapic nolapic clocksource=pit