Limiting bandwidth globally and per user

[Rend.net Webmaster]

I am the admin of a school proxy.  We have a t-1 link to our upstream
provider.  Our main problem is particular people hogging too much of the
bandwidth.  I want to know how to put a limit of lets say 100K a second on
global access, and 15K a second on particular users.  I was told something
of using the delay there.