You will need to put the sysprep files onto the VMware Virtual Center server. They go in “c:\Documents and Settings\All Users\Application Data\VMware\VMware VirtualCenter\sysprep”. You’ll need to download the Sysprep for Windows 2003 and put it in the svr2003 folder. You can then use the deployment wizzard to change the name.
Personally I setup templates and have the templates setup to use the name that I give the virtual machine in the first step of the wizard.
If you are going to have Windows XP guests you do not need to put anything in the xp folder. It uses the same sysprep as Windows 2003.
If you will use Windows 2008 or Windows Vista as the guest OS you will need to use the latest version of ESX (3.5) and Virtual Center (not sure the newest version).