This is a bit of perhaps tooting my own horn, but since the content is so apropos, I hope that won't be too big of a deal. Anyway, a few days ago, i finished an article that is an SNMP primer, both as a general look at SNMP, and some tips on using it with Leopard/Mac OS X 10.5 Server.
The article is called, appropriately: A Primer to SNMP on Mac OS X 10.5 and Mac OS X 10.5 Server
Hope it proves useful.