[Freaken]

DD-WRT allows you to do this using its QoS service. You can specify rules by range of IPs or by MAC adresses, so this definitively is possible.

You can also set rules regarding specific groups of services (games, torrent, netflix, etc.).

If you want a more powerful way to control your bandwidth, DD-WRT has iptables installed, which can be configured by connecting to the router through SSH. The possibilities using iptables are pretty much limitless, but there is a level of complexity that is completely abstracted when using the QoS service.

For more information, see:

http://www.dd-wrt.com/wiki/index.php/Quality_of_Service

http://www.dd-wrt.com/wiki/index.php/Iptables_command

[Alphasite_]

Or, just use the Asus' own QoS system.The newer routers actually have a fairly fancy one. But neither of these has a way to limit directly by interface, do they?

[bestham]

Tomato by Shibby can use QoS on vlans, and that makes it possible to apply traffic shaping on different interfaces.