We could argue all day about whether Mr Gates and his greedy monopoly has the right to invade our computers. There are lots of opinions, mine is ***** Microsoft if they feel it's ok to play a dirty game then it's OK for us to get at them any way we can.
Go to http://windizupdate.com/ for all your windows updates without fear of Microsoft planting any spyware into your system. You can't use Internet Explorer for the plug-in you must use Nestcape or FireFox.
I accidentally picked up the WGA file and simply did a re-install then found one of the many non-Microsoft Service Pack 2 downloads. It's a huge download, around 200mb but worth the hassle if ServicePack2 is compatible with your system (a lot have trouble with it, I haven't). I believe most of the problems with SP2 occur if you have other applications running while attempting the download.
I can't remember where I downloaded it but there are many legal non-microsoft sources just surf around you'll find it.
There are a few ways of avoiding or removing the WGA spyware without doing a re-install, I just found it easier to do the latter.