http://www.roaringpenguin.com/pppoe/
I dunno if that'll work, but they do have an Alpha release and it's known to work in one or two of the BSDs, so it's worth a shot.
Depending on the provider, and the needs of the machine firewall and NAT server wise, I might be able to get ya a router if you're looking to spend 40 or 50 bucks. A co-worker of mine used to work for telco and has quite a few low-end DSL bridges, but these particular bridges were re-branded as such by the manufacturer, Efficient Networks, because they couldn't make enough bridges to supply demand so alot of them are actually routers, and need only a firmware swap to enable the router functionality.
Problem is they have no DMZ, only handle DHCP for up to 18 machines, and can only support up to 64 NAT entries. If your provider is using PPPoE on a DMT encoded line, though, they will work.
Xayd