Good news first: I managed to fix the Driver_irql_not_less_or_equal ndis.sys blue screen of death error. The bad news is that I'm now even more puzzled about my computer than before.
What I wanted to do was a simple reinstall of Windows XP Pro. So I put in the CD, press the F12 button at start-up to go to the boot selection menu, select boot from CD. Windows XP CD boots up, and after loading a bunch of drivers and stuff goes to the first screen, where you have to press Enter to continue. Only pressing Enter doesn't do anything. In fact no key does anything, it seems among all the drivers he loads there isn't one for the keyboard. And I tried both a USB keyboard, and a classic PS/2 keyboard. Several times, connecting and disconnecting keyboards, and rebooting. But while all the keyboards always work in the boot menu, none ever does in the Windows XP setup menu. I'm stuck.
So I try something different, boot my computer from the hard disk, but in safe mode. Then try to run the Windows XP CD. It runs, keyboard works, but when I tell him to install, he refuses. My Windows XP CD is service pack 1, while the installed version is service pack 2, and he claims he can't install an older version over a newer one. Fortunately when service pack 2 came out, I asked Microsoft to send it to me on CD (for free). So I put in my Windows XP service pack 2 CD, and install that one. Now this doesn't do a complete Windows reinstall, but it does install a large number of files, and luckily for me, whatever was broken in my computer before is fixed by that. No more blue screen of death, and the video editing software that wouldn't run last weekend due to driver problems is now running perfectly.
I'm just worried that if the computer crashes even worse, I won't be able to do a full reinstall, due to the keyboard not working in the Windows setup. And why doesn't it work? Is that some trick from Dell to prevent people from installing whatever they want? Or is my Windows XP Pro CD too old to work with my current hardware? I'm puzzled.