Hi dude! Squid is a good proxy, though you may like another variant of bandwith control. It's called traffic shaping.
You may read about it here:
http://lartc.org/
and more conretely here (by the way, I used this manual to shape the traffic for my users) :
http://luxik.cdi.cz/~devik/qos/htb/m...rg.htm#sharing
And speaking about Squid, it's a good documentation here:
http://www.squid-cache.org/Doc/config/delay_pools/
http://www.squid-cache.org/Versions/v2/2.7/cfgman/ - for v.2.7. Scroll down to the heading ' DELAY POOL PARAMETERS'
PS: I do not use delay_pools, I use shaping. If you need, I may send you my script with shaper rules. Just contact me via PM.