I have it running on an always on Linux box that sits on the LAN. It monitors the router which is also always on, as is the cable modem.
IOG is primarily aimed at *nix type systems, but it could be forced onto Windows. IOG is the easy part, the harder parts are that it needs perl, apache, and cron - things not typically found on Windows machines.
The first thing you should do is verify that your router can be monitored via SNMP.
On my Comcast connection, there is a constant amount of traffic on the WAN port, amounting to about 4MB of per hour.
Our router is a Linksys E4200, which, according to the Googles, does _not_ support SNMP. The Motorola SB6120 cable modem, however, does support SNMP...unless Comcast has it disabled.
I run Ubuntu 12.04 on my desktop, so...no problem.
OK. Just run snmpwalk on the modem's IP address. Coming up with the community string will probably be the gotcha unless it is the default of 'public' or it's documented somewhere.