[link|http://www.pcguide.com/ts/x/sys/beep/index.htm|This] seems to be the best description of them that I've found yet.
I've got a Tyan Pentium-233 motherboard (Tomcat 4, S1564) which runs fine with 64 MB of RAM, but won't run with anything higher (tried multiple varieties of SIMMs, etc.). Never figured it out. :-( I hope that doesn't bite Brian.
Cheers,
Scott.