Well, the issue is sorta fixed, I'll explain myself :D
So, I did what Carol suggested, rebooted, and when I came back in, Windows tried to install the drivers. I could not stop it, but the OS threw an error box telling me they could not be installed. Fine, I disabled the ports again, Windows threw another error, it needed a reboot to disable the Ethernet ports. Rebooted, and the same situation repeated. Then I opted for reinstalling the drivers directly from the CD, with the result of the error I mentioned above, Windows could not find a certain file. OK, I said to myself, I shall delete it altogether. Uninstalled the nForce package, rebooted, and... a black screen.
Windows loaded, but nothing appeared in the screen, I could see and hear the drives loading the system, but nothing was shown. It was very weird, because I saw all the booting process with my eyes. OK, let's try with safe mode. It reached the logon screen, and when I grabbed the mouse, shivers went down my spine. The cursor didn't move. I tried with the keyboard. Nothing. I checked the batteries, and they were charged.
So I grabbed the nearest Linux Live CD, copied all data to the secondary drive, and formatted. Everything is fine now, no "scheduled" hiccups, and the TCP/IP protocol is where it should be. What's more, everything seems to run smoother now, I don't know if it's because of SP3 (which I didn't install before), the lack of all the cruft of more than 150 individual updates, or that something was really broken, either by my hand, software misbehavior or malware action.
I think it's difficult the TCP/IP absence was caused by malware, because I did not saw anything with the analysis tools, and all scanners did not detect a single thing as well (apart from tracking cookies). Maybe I caught something new, and borked everything, which could be the case, as the other day I found myself without administrator rights (solved by a reboot).
Funny enough, in other of the forums I hang around, people were complaining about this same problem, in this caused by the action of Microsoft updates, which was not my case (as I did apply that particular update after everything went berserk). Most probably something was wrong with the LSP, as lanux suggest, so I'll bookmark the thread for future reference. Thanks guys :)
EDIT: Rephrasing, typos, etc.