While a full Vista SP2 CD (that CD with just the SP2) could help I have yet to see any solution that required less time than what you are doing now.
Put another way, you could download and script the installs but how many days would you invest in this?
Also, the HP's I've used let me make the Restore Media. I STRONGLY SUGGEST YOU CREATE THESE BEFORE ANY UPDATES.
My father has a Vista machine (HP) that is 4 years old and needed a fresh start. I ran the recovery to restore the factory image as there were no Vista discs. Is there a way to tell Windows to just keep checking for updates until it finds none? I now have to install them, restart, check, install, restart, etc. I want to be able to just have it run without touching it. Perhaps this could be done via a script, but I haven't figured out (or looked up really) how to call it.