Here's the clip of a post I found that worked for me. I had an IBM T60 that I restored to factory image. I downloaded and installed XP SP3. Then the windowsupdates seemed to stop working. The fix below worked for me.

Click Start, select run and type the following (pressing okay after each one):-

net.exe stop wuauserv
regsvr32 wuweb.dll
regsvr32 wups2.dll
regsvr32 wups.dll
regsvr32 wucltui.dll
regsvr32 wuaueng1.dll
regsvr32 wuaueng.dll
regsvr32 wuapi.dll
regsvr32 MSXML3.dll
net.exe start wuauserv

Try WU again.

reference: http://forums.techarena.in/showthread.php?t=966195