how can I limit each computer's bandwidth through my router?

I have Comcast internet, and we are supposed to get 3Mbs, but one of my room mates frequently downloads large video files, and I was wondering if there is a way to divide up how much bandwidth each computer gets.
We all connect through a US Robotics 8054 router through ethernet connections. I am just looking for some way to set it up so that when no one is using the internet, my room mate can use all the bandwidth, but when another computer tries to connect it automatically splits the bandwidth by the number of computers connected.
I thought that the router should automatically do that, but I guess I am wrong because when I try to connect while he is downloading, I download partial pages, or pages that normally download in about 2-5 seconds take around a minute to load, and sometimes don't even fully load. Thanks.

 

Entry Level Cable/DSL Router can not do it.

May be this can Help: Can I Monitor my LAN, control the usage of the Internet, and Network Resources by other computers from my main computer?

 

Thanks, I have an extra computer, and have been thinking about doing something with it, so I will probably just turn it into a linux router. Now I can solve two problems at once, get a use for an old computer, and equalize the bandwidth between all of my computers.