DSL modem weirdness

[Z]

I think (I hope) I finally resolved it with a bit of searching - basically the machine was querying for the DNS server, getting some funny responses, and as a result cutting the connection to keep things safe on the computer end. Hard-entering the DNS addresses for the ISP seem to have resolved the problem. The same or very similar situation is described here and led to what thus far appears to be the solution (should anyone else be plagued with similar problems in the future...):
http://forums.macosxhints.com/showthread.php?p=526879