So I got roped into helping my dad set up his home wireless network. The thing is that he has no concern about leaving an open access point, and I've tried to convince him of the risks that such an action runs. He's started to get it, but I'm still working on him.
Anyway, I started futzing with David's laptop to play with it, and discovered that it was hopelessly infested with spyware, and completely unpatched. Well that took precedence, and I installed adware, contacted Microsoft update, and began to clean house. (The phrase 'David we really need to talk later about computer hygiene' was uttered at least a half dozen times) So after the first couple of security updates, and a pass with spyware removal, I rebooted. And when the system came up there was no longer any networking.
Now as I said, I was looking at securing the wireless network, so there were a whole host of issues that could have been wrong, and it took me hours before I got it down to realizing that XP just wasn't receiving any packets. Anywhere. Of course failing to connet with an actual wire in the back also leant some evidence to that theory.
So I figured I'ld remove the networking interfaces, reinstall them and go from there. Of course windows doesn't let me do that because it had some messed up network bridging in an impossible state. (Kinda like the sofa in the staircase from Dirk Gentley's Holistic Detective Agency). Anyway, another dozen reboots and I found the right keystroke to send me into safe mode. I removed the interfaces, rebooted, reset them, and still nothing.
During this I had been downloading SP2 on a separate computer, and was trying to work out the right way to move it to a machine that didn't network. With no CD-Rs, I wasn't looking to kindly on 200+ floppy transmissions.
But again google came to my rescue. With the right set of keywords ("windows xp 'not receiving packets') I found a thread in a forum somewhere informing me that some spyware took a scorched earth policy towards the TCP/IP stack and left the computer completely unusable. (For future reference you want to do a google search for "winsock tcp fix" if this ever happens to you).
That fix fit neatly on a 64M USB keyring drive lying around the house, and so now I am able to leave my brother's laptop alone in a pareto optimal state from when I found it.
I'm so glad I don't have to worry about spyware when I compile eveything from source.