Hey guys,
I thought I’d just share a nice and yet powerful tool that I’ve used for quite some time to restrict certain IPs in my network to certain speeds at the WAN interface of my WRT54GL router. It has been written by robsonn from the HyperWRT forums.
This tool creates scripts using the tc-tool in order to shape bandwidth and allocate preset speeds to different users. Allocation works via MAC- as well as IP-addresses. You can limit both down- and upstream, depending on the firmware you use for your WRT54* device. I am for instance giving my sister’s pc via static dhcp a fixed ip, which in turn i give 8000kbit down- and a rough 192kbit upstream. at 16000/1024kbit, that leaves me with enough freedom of bandwidth for when I host a game of Warcraft III, play any other games or the likes.
It’s a nice addition to QoS.
Here’s a download link that I mirrored on my server. If it doesn’t work, try the link from the first paragraph. That one’s probably always going to be more up-to-date.
julian's techblog 
this by the way can be considered deprecated – Victek’s RAF Tomato mod has this function integrated into the webui. check it out here:
http://victek.is-a-geek.com/tomato.html