Johno, no disrespect to you but I may have a better option for you and others...
OK, Ive tried loads of patches fixes and workarounds, and none of them working or last 2 minutes.
BUT I have found one which does the lot, that is allows you to do the following:
get security updates
get other related updates which arent vital
get all downloads from download centre regardless of WGA validation...IE7,WMP11 etc
Install downloads without 'this product key is not valid'
No nag screen or little star on ya system tray
All without needing to change your product key.
Program is called MUBlinder v3.2 and is a small prog which mods WGA dlls and thats it.
Where to get it, apart from demonoid, mininova etc
CODE
http://www.p2plife.com/forums/index.php?showtopic=320
you wont be disappointed (i feel like a sales rep, i'm not but just glad to get one up on m$ :f*@&%:)
BTW no spyware or any of that shit... runs once at boot time (just to check for new WGA updates) and shuts its self down