Service Pack 2 woes

OK, so I sent my computer in for repairs, and I have now a new harddrive for
it. The computer did not have Windows installed, so I used my disks from when
I first bought it (in June 2003) to install Windows. After it installed, I
went to download Windows updates. So no problems, until I reached the Service
Pack 2.

First, Service Pack 1 didn't download, I don't know if that is relevant.

Second, it downloaded fine, I think, and when it was installing, it froze
halfway for about 3 hours. I asked on these forums what to do, and they told
me to exit windows, and it should resume. ...well I eventually did, but when
windows started up, it showed me a blueish screen saying recovering., or
something or other, and now I am getting:

"The Windows Service Pack instalation did not complete. This system is in an
unstable state. Go to Control Panel, Add or Remove Programs and choose to
uninstall the Windows Service Pack, or contact your system administrator."

The service pack didn't resume installing, and when I see the threads about
removing the service pack, the errors scare me x.x I don't mind reinstalling
windows, but if this happens again...