Because Microsoft won't let Firefox access the Windows Update site, you have to use Interpants Explorer
Microsoft apparently don't think users with questionable copies of XP should access it either
Anyway, a simple solution.
1. Download Trixie
2. Save this userscript to your Trixie scripts folder (program Files >> trixie >> scripts)
3. Start up I.E and go to Tools >> Trixie Options
4. Make sure WGA Workaround is is checked
5. You should be all sorted
