Windows XP SP3 breaks Windows Update
If you install XP SP3 on a clean SP2 box Windows Update will no longer work.
Unless you have the newer Windows Update Agent 3.0 your stuck in a hole
There is no way to get it via AU or WU or MU only a manual installation can resolve the issue
1. Download the new Agent (but do not Run it yet) to your Desktop (so you can find it below) :
X86 Version: http://download.windowsupdate.com/WindowsUpdate/redist/standalone/7.0.6000.381/WindowsUpdateAgent30-x86.exe
2. Start, Run, CMD
In the black box:
net stop wuauserv
"%userprofile%\Desktop\WindowsUpdateAgent30-x86.exe" /wuforce (don't forget the quotation marks)
net start wuauserv exit
Thanks to Bill Castner for putting me onto it.