I built a very similiar box recently myself, MZ. WinME, Athlon 1.4 T-Bird, same mobo, not nearly as much RAM B-P
I got the dreaded beeps myself, though mine actually ran at first. Then it would slowly destabilize and whether or not it would reboot was random chance. Eventually, it stopped rebooting at all. Beep, beep, ad nauseaum.
Turns out I didn't stuff my RAM in the slot tight enough. DUH.
Another difference is I'm also running a GeForce 3, rather than a 2. It's been giving me fits. It's a blazing hot card, but incompatabilities and crash bugs with some older games are apparent. After your post, and several hours of tweaking trying to unscrew Half-Life, I'm pretty convinced it's ME. ME was all I had when I was putting it together, though. So I dealt with it. Now I have a copy of 2K Pro, but I'm loather to either install it over ME (bad bad karma to install Windows over Windows) or to suck the 12 gigs of crap that's already accumulated on my HDDs out and reformat them. (Where does it all come from?) Anyway, like the rest, I'm glad you got it straight. Headaches aside, it beats buying some crap generi-box from Best Try, that if you want to not suck you'll have to dump a grand into anyway and hope the fucking proprietary case design doesn't screw you.

TRB

"You are... what you do... when it counts." -The Masao