Also volume licencing has changed since WinXP, cannot say when it changed though as never looked into Vista licencing, but you no longer get a volume licence key you will get the choice of a MAK key which only has a certain amount of activations or you will have to use a KMS server with a GVLK, this will require the PC to contact the server every 180 days. My suggestion would be to go with the MAK key as its only 30 computers it should be quite easy to manage.