Check out cacti, it will do SNMP pulls on the host. Both bandwidth and process. Its not a simple app, but very useful. Also if you have firewall setup on the box, you should be able to get stats on the ports/protocol.
Have you ever used very basic snmp? I recently discovered the snmp command line programs (by the mechanism of typing "snmp" then tab twice into a terminal window) but I haven't yet been successful in pulling any values out of an snmp mib. The commands correspond exactly to the datagrams specified in the snmp rfc though, so it can't be all that hard to use them.
Regards, Max.