No offense guys, but I guess I didn't make myself clear. I know WHAT to do, and HOW to do (most of) it. I just wasn't sure I could figure out how to create the custom error page and make it do what I wanted. Turns out, I could! And it wasn't as complicated as I thought.
Doing what I do best, I reverse engineered a couple files and cobbled together what I needed. I started with the page leatherlips linked above, added some code stolen from ruirib's email spam MOD, and came up with this:
Custom Error Page
It has a general error page with a 404 error include. I'll add additional error includes later.
It doesn't log to a DB, but it does email an error report.*
So? What do you think? Not bad for an amateur?
*The file in the .zip emails the report to the forum webmaster. For this demo, I changed that to a dedicated email address to keep from clogging my inbox.<