What do you mean? If you are running either ESX or ESXi, if you log in with the vSphere Client, you can see the "build number" and version of ESX/i. If this is a new install, go the IP addy of the host which will bring you to a web page with the vSphere Client download. Install it, then log into the host with the root account. Once logged in, you can see the version/build #.
Regards,
~coolsport00
