I recently had opportunity to install VMware ESX on some old Dell hardware. These notes helped me move through the process.
VM-Help database of links: http://www.vm-help.com/esx/esx3.5/Whiteboxes_SATA_Controllers_for_ESX_3.5_3i.htm
How to enter nocheckCPUIDLimit on ESX with screen shots – http://communities.vmware.com/message/1136449#1136449
This is a two step process. Once for initial install from cd-rom and once for rebooting off hard drive. I did have to tweak it as it did not work 100% as advertised (see BrennanB post on April 27th).
Please let me know what other links worked for you and your old hardware. Be sure to update vm-help with any feedback too!
I b e n