Question : Vista is "stuck" using KMS server, and I can't make it do online activation

How to I convert Vista Enterprise to use online activation (not KMS) using SLMGR?

Answer : Vista is "stuck" using KMS server, and I can't make it do online activation

Read through.....
http://technet.microsoft.com/en-us/windowsvista/bb335288.aspx
Especially the sections...
Steps to convert from KMS to MAK
Steps to convert from MAK to KMS

It can be done using either the Change product key GUI or slmgr.vbs