I need to give game ports highist priority

Hi guys
I have a customer that plays Counter Stike on ports 27015 thru 27030 and every time some other customer starts down loading or uploading files it makes his ping time jump from 50 to 200. Is there a way to give the ports higher priority so this will not happen or is there a way to devide the bandwidth equaly between the the customers with a little extra left over so the internet connection wont bog down?
Example: I have 1meg up and 5.5meg down. If only one customer is online transfering he gets 800k up by 5megs down. If two customers are online transfering they each get 400k up by 2.5megs down. If four customers are online transfering they each get 100k up by 1megs down.

I am leaving the extra bandwidth unused because we are using muxed ADSL and if you fill up the upload on a ADSL line you will watch the pings sky rocket.
OH, And yes the lines are bonded up and down to make one big fat pipe!
Huyen