I've tried deploying Win 7, Win XP and Win XP x64 templates. I've manually entered the product key during customization and I've also tried putting the key in a Customization Specification. No matter what, when I boot up the deployed VM for the first time it asks for the product key. Additionally, I've noticed that the user name I customize also doesn't stick. However, the new netbios name DOES stick. I wonder if this is related....
Did you copy the sysprep files to the ProgramData directory on the vCenter server?