I found one on craigslist for $15 but want to make sure it will work, or if I do get it and try to install it I want to make sure I don't break my computer.
I did some digging and yes it will work. If you really want that thing to run fast you could put a dual core 2.0Ghz G4 in it. But they cost a lot more then $15. Your find is a pretty good one. I would say go for it.
maybe yes, maybe no. depends on the AGP systems Uni-n rev. some were made with a rev 3 ASIC chip which prevents the use of dual cpus.
more info (and an easy way to check) HERE. this document (pdf) is from sonnet, but the problem with chip revs would prevent you from using an oem dual as well. test first, buy later!
I had an AGP graphics from back in the day, which was a stock 400mhz. I swapped it out for a dual processor from sonnet. Maybe I was a lucky one, though.