Windows reboots immediately when I start iTunes

Question

The Problem: When I click on the iTunes icon to start up the software, my computer restarts IMMEDIATELY. There is no error message, the computer does not freeze, and there is no indication that an iTunes window opened at all, even briefly. The screen just goes black and the boot information comes up right away, as if I had pressed the reset button on my case.
My Computer: My computer is a custom built windows XP Pro, SP2, 1G RAM, 2.2 Ghz AMD processor, 3 hard drives -- the bootable drive (C:) is 4G with about 1G of available space and runs at 7200 RPM. The other 2 drives are large (~80G each) and also run at 7200 RPM.
Attempted Solutions, so far: I have spent hours on the phone with Apple support about this already. They walked me though the msconfig process (turning off all other processes and rebooting), I have uninstalled and reinstalled iTunes, Quicktime and Quicktime standalone many, many times. Obviously, nothing has worked, since I'm posting here that I still have a problem.
I have also run regclean, updated the Windows Installer, updated my Virus checker (Avast), and installed and run ewido (no malware detected--I keep a clean computer).
Ideosynchracies and Notables: 2 things are important to note.
1) The very first time this happened, I tried to uninstall iTunes and reinstall. I went into the "Add and Remove Programs..." dialog in the control panel and hit "Remove" for iTunes. Nothing happened. I rebooted and tried again. Still nothing. Only after mucking around for a while and trying to install over top of the existing iTunes, etc. did I finally get it to uninstall. That was iTunes 5, which came on the CD with my iPod nano. Henceforth, I have been working with iTunes 6, downloaded from Apple's website instead.
2) Even before I had a problem, iTunes opened successfully. In fact, I have opened iTunes 3 times successfully. Each time I have been able to open it has been after a clean install of the software. That is, I uninstall the previous copies of both iTunes and Quicktime, reboot, install Quicktime standalone, uninstall that, reboot, reinstall iTunes+Quicktime, reboot, and then open iTunes. It works! (Yay.) But then if I close iTunes and try opening it again, my computer crashes right away (described above). This occurrs whether I reboot between the 1st time and 2nd time or not. If I do not uninstall iTunes completely (and Quicktime), then reinstall them fresh each time, I can't open iTunes. Since this process takes about an hour to accomplish, this is clearly not an acceptable way to use iTunes.
Ultimatum: I will not reinstall windows XP. That is a 40 hour task I am not willing to undertake. In addition to the numerous games I have installed, each of which requires multiple patches to be applied after installing off the CD, I dislike many of the default configurations of Windows and it takes me a while to go though all the settings and change them to my preferences.
Additional notes:
- My OS (Win XP) is an upgrade from Win 98. This should not make a difference, as the upgrade was done over a year ago and I've never had any problem. Nevertheless, the tech support on the phone told me that this was probably the problem and that I needed to contact Microsoft to have them solve my iTunes crashing dilemma. (Yeah, right. I told him there was no way he was pinning the blame on MS for this, since it never happened until I bought an iPod and the crash only occurs when I launch iTunes).
- Before my iPod, I hated Quicktime for the nasty things it did to another computer of mine (basically, when you install it it leaves bits of itself behind that run in the background and report things back to QT. This was years ago and maybe it doesn't anymore, but it left a sour feeling with me, so I avoid QT when I can now--Real, too. Same problem.) So instead of Quicktime, I used to use a program called Quicktime Alternative. It's basically the codecs for QT, but without some of the bloat. I've used QTA for nearly 4 years now, in various versions, and never had a problem with them, but it is conceivable that there could be some bad interaction between the real and alternative versions of QT. However, I removed the QTA from my system, and have installed and uninstalled the real QT many times now, and opening the real QT browser does not cause any problems on my machine.
My thoughts on the matter:
- Since iTunes can start up successfully after a fresh install, but then crashes once I close/reopen it, I'm thinking that there's a setting that it's trying to set after the initial installation. It would probably be related to registration or something like that. I'm not sure what iTunes tries to do after the first use, but the problem could be with that. (On first use each time it asks me some personal information and gives a "Welcome to iTunes..." message. It is likely that after that, it tries to store 1 more setting somewhere and that's what's causing the problem.)
- Since iTunes crashes the whole computer (not just itself), and the crash happens IMMEDIATELY when I click the icon, I'm guessing there could be a conflicting registry that is preventing iTunes from opening, and in fact sending a reboot signal to the OS.
So, any one have similar experiences, proposed solutions or other helpful advice?
*here's hoping...*
self-built PC, 10+ yrs experience w/ Windows, 1st Apple product   Windows XP   iPod nano, iTunes 6, 2G RAM, 2.2 Ghz CPU

Answer 1

I typed WINVER in the RUN option, and it shows Version 6.1 (Build 7600).  It does not say Service Pack 1.  I check the other computer I share iTunes with and it shows the same version/build.