This is getting annoying, to say the least. First the Nvidia driver I
downloaded from the Nvidia website was the wrong one, despite clearly
choosing my video card from the list. 1.0-9755 doesn't support my card, so
after a little searching I found I had to download the 1.0-96xx version.

Downloaded, run that with the sudo command gets me an error that says "You
appear to be running an X server. You must Exit X before installation can
continue, or some such nonsense.

Next obvious question: What is an "X Server" and where do I find it?