Out of the websites returned by that Google search I would use Paul Thurrott's instructions (this one) as the first one has an error in the command line.
I use nLite to customize my Windows CD's. It is very easy to use for a simple service pack update. You might as well integrate SP3.
You can also customize install options, automate the install, integrate drivers and IE7. The site also has guides for using nLite and links to integrate many popular programs like Adobe Reader. I also recommend Windows Media Player 11 slipstreamer to integrate the latest WMP and hotfixes.
The downside is that you need a Windows PC to use these integration tools.