Dividing the bandwith between the LAN computers

Hi there. I wonder if someone could help me with this problem:

Is it at all possible to divide the bandwidth between computers in a LAN connected to the web?.

At home we have a LAN of 2 computers with a 256 Kb ADSL connection via router. Everything is set up propperly and both internet connections work fine.

The problem arises when a computer is downloading a file from the web. It sucks all the bandwidth, don´t letting the other one to browse with a decent speed.

Are there software tools to force a division of the bandwidth by half, so both computers can have the same connection speed, no matter what the other one is doing?

I hope someone points me at the right direction. This problem can cause major argues at an otherwise quite peaceful home...

Thanks very much for your time.

Jose