Or WRT54GL
Your broadband modem will have an integrated router in it. Usually the address is 10.1.1.1, 10.0.0.1 or 192.168.1.1... try one of those in your browser and you should get to the router's/modem's configuration page. In there, you might be able to find settings for "quality of service" (or just QOS for short) (not many modems have this, IDK if yours does, but it's worth a shot), which basically allows you to set download/upload limits based on different criteria like source/destination ip/port and even stateful packet inspection (=magic that determines the type of traffic, goes by other names too).
If none of the above addresses work, go to the command prompt and type "ipconfig" and find your default gateway address. That's the one you should be using to get to the setup.