When several computers share a single broadband connection (some wirelessly), is there a way to set a user-defined upper limit (either in absolute Kbps/Mbps or relative %) on each one's bandwidth usage?
This might help: http://www.linux.org/docs/ldp/howto/Bandwidth-Limiting-HOWTO/ Your firewall probably inplements something like this. nitro
There are both software (installed on each PC, ex: http://www.netlimiter.com/) as well as hardware (routers with QOS features, ex Linksys RVS4000) solutions to this depending on which way you want to go (and how much you are willing to pay)
what kind of wireless & router do you have? The cheap stuff you can't do much with but the more expensive stuff have the options.