I really need to know

I won't lecture you on the anti-social nature of what you are contemplating... ;-)

Here's another idea though, but how well it works depends entirely how your particular network is laid out. If it is possible to segregate that one host onto a single interface at any point, you can then reduce the MTU used by that interface to something relatively small (compared to the 1500 that is standard for 10Mbps ethernet). Try 576, or 296. Less than that might be too drastic but you probably could even go less than 200. If you can't segregate that one host, just reduce the MTU for the common link to the Internet to 296.

Note that the effect (especially at 576) might indeed be nothing at all! If both of you are using it at once, and the connections that you each have already has a 'path mtu' of 576 or lower, there will be *no* effect.

Most likely, even at 296 your roommate would never notice it! Normally the only effect is increased overhead because each packet has the same overhead as before, but carries a smaller payload. That will reduce his throughput slightly when he is the only one using the link.

But the desired effect, when you are both using the link, is that *your* packets (which are still large if you can segregate his host to a separate interface) get equal opportunity, so if you both are sending a file, for example, if his packets are 296 and yours are 1500 bytes, obviously you get more bandwidth. The other effect is you wait 1-5th as long to get a packet queued for transmission, hence interactive response will seem greatly improved (and that will be true even if it is a common link that has the low MTU).

Now you'll have to think of an excuse to reconfigure the entire topology of your network, putting *everyone* onto a separate configurable interface (as opposed to a hub or a switch) so that you can "manage" the bandwidth.

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