limited or no connectivity

Problem
A friend told me he has problems with assigning IP addresses. I was so curious how this happens. He always receives error messages saying "Limited or No Connectivity" whenever he connects it via wireless, plugging in a LAN cable or just connecting using ADSL.

What I Did
1. At first I suspected it was the drivers of the network devices. After checking the driver versions and reinstalling it, it didn't do any help at all.
2. I checked to see if the TCPIP.sys file was corrupted. Replaced with a fresh file from the installation disc, restarted and the error was there.
3. I used a tool called WinSockFix as I was reading another problem faced by another person. Downloaded it, ran the tool and boom... it works.

What Was The Problem
I don't really know what happened. After reading what WinSockFix does, it was repairing the registry relating to network entries. Hmm... Interesting. Some theory suggests it could be malware (virus, spyware, trojans, etc.).

Alternative
At first I wanted to reformat and reinstall Windows XP again. That would be the easiest solution but the most time consuming of all. Luckily if it wasn't for that post, I would stare in front of the PC and wait for it to complete installing.