Monitoring traffic at router level?

I have a MN-700/720 set-up which works well. Three
computers (HP Pavillion, XP Home, SP2)(Apple G4 OSX)(HP
laptop, XP Home, SP2) and a Linksys router for VoIP running
through the base station. My question is how to monitor
traffic/bandwidth at the router level, preferably with a
graphical display.

I found a third-party program which seems like it would
fill the bill - PRTG - but am having problems setting it
up. Does the MN 700 have SNMP? What is the IP address? (I
assume it's 192.168.2.1) This is from their help section:

"Is SNMP installed and enabled on the device? (see
configuration of the device)

·Does your machine running PRTG Traffic Grapher have access
to the SNMP connection on that device? (see device's
security settings)"

Taken from manual of PRTG Traffic Grapher © 2003-2004
Paessler GmbH, www.paessler.com

I believe this issue would be of sufficient interest to
500/700 users that it merits discussion in this forum.

TIA for any information.