And I've an update: I decided to have CCleaner and Tune-Up Utilities kick my computer's [bleep]. That is, between the two, I ran every single clean-up and fix utility...even the ones we're generally told NOT to run.
I then removed the last half-dozen programs I can recall downloading (or that updated) just before all this started. These included an MKV to AVI converter, Quicktime, several DivX programs, and something else I can't recall just now.
The computer is ALMOST back to normal. Still a slight slowdown going on, but I'm only noticing it now on playing audio or video (about 1/25 of what was in the MP3 file I posted), and I no longer notice it when launching programs or in the movement of the mouse and such. I'm guessing something I'd downloaded got corrupted (and perhaps was corrupting other things? What do you think?)
Edited by Phlegmbot, 16 January 2009 - 01:11 AM.