We do work on a lot of environments which have VMWare Virtualization. The first thing that needs to be done is to find the version of the ESX in use in the environment.

If you trying to seek Microsoft CSS support for a non-Microsoft virtualized environment, then you need to be aware of the Virtualization Support Policy:

http://support.microsoft.com/kb/897615

Also if you want to find out if your virtualized environment is supported, then you can use the Support Policy Wizard.

Here is link for a step-by-step guide to find out the ESX versions and builds:

http://www.techhead.co.uk/how-to-determine-the-vmware-esx-or-esxi-build-version

Reference articles:

Determining detailed build number information for VMware ESX 4.0.x hosts

Determining detailed build number information for VMware ESX 3.0.x and 3.5.x hosts