VM Templates and Windows Licensing

I recently had a frustrating problem cloning a vm. It just wouldn't sysprep using either the customisation tool in vsphere or manually in Windows. Doing a little digging I discovered the rearm count was down to zero. Presumably the vm was a clone of a clone of a clone! (This vm has been around longer than I have here!)  There's a useful command to check the rearm count if you are planning on cloning a machine and aren't sure of it's history

Cscript c:\windows\system32\slmgr.vbs /dlv

I did find this blog, which is useful:

http://option9.blogspot.co.uk/2009/06/getting-around-windows-rearm-limit-with.html

However I couldn't get the SkipRearm reg key or xml update to work. Luckily I had an alternative machine I could clone this time...