I actually dealt with this situation recently as I have a somehwat differenct situation with my home network.
I have a cable conn 30mpbs down and 2 up, with 14 users on it.
Everyones got a phone, a lot people try to watch netflix, and all sorts of shit goes on on my network, pandora, P2P, you name it it goes on.
I got to the point where I couldnt watch anything hidef because of constant buffering.



I got frustrated, read up, and bought an e3000, flashed it to DDWRT.
(I said I have a different situation and this it it... I am the "manager" at a "sober house" and the network is available for the residents to do "job search" and "productive shit" but we all know how the mice play when the cat is... well... in the other room.)
I thought that I would be able to limit bandwidth by MAC address, and it turns out that short of learning how to script for these linux open source software routers with IPTABLE scripts, it's kind of sketchy (read: takes a lot of learning.)
Heres what I did to TOTALLY CAP AND RESTRICT EVERYONE IN THE HOUSE.
(except for my host machines and the other managers host machines.)
It works very well, please use this with discretion however as you will be in pretty much complete control.
1. QoS on any router does not actually limit bandwidth, it only changes that way the router buffers and prioritizes frames/packets that are flying back and forth. SO, in other words, even if you are set to HIGH pri. and they are set to LOW, and they are streaming 10mb down with netflix, you are going to have hell trying to get some good response out of it.
Here is how I setup QoS on DD WRT with my e3000.
Flash your router, go into QoS page after it is setup.
Put everyones MAC ADDRESS into the QOS table including yours.
Set everyone elses priority to "BULK" and yours to "EXEMPT"
Scroll to top of page and check QoS and use either HFTC or HT? i forget that third letter. (these are 2 dif types of QoS)
VERY IMPORTANT__**** Now you have to set a DOWN and UP limit. This is a hard limit for ANYONE that is on the QoS table that is not Exempt.
I set mine for 1.25 mbps down and 600k up for everyone.
(myself and the manager are exempt.)
VOILA-
Everyone on the network is CAPPED at 1.25 down and you and the other exempts should be downloading at full speed, AND your packets will have priority over theirs.
Good luck with your throughput limiting adventures.
Oh, and by the way, those routers do suck. n150n or whatever it is you have.
I recommend the e3000 cisco/linksys (50$ refurb) if you want DUAL RADIO,
or the RT-16 ASUS i believe it is if you want a N single radio.