If you've already started it installing you have one more chance:
Click "I do not agree"
If that already went by and you get this when you boot up:
Click Cancel of course.
You don't want to have to do that every time you boot so after it's closed go to this
download page and download Sysinternals' Autoruns.zip
Unzip it and run it and click Scheduled Tasks and uncheck the WGA entry.
Click Save. Fixed.
The Download********************************************
Rock inadvertently got to the screen above in a XP virtual machine I had him
using when he last visited. I just ran the Autoruns and did the above steps.
Booted, All clear.
Thump