Traffic Shaping

hy im from romania i use m0n0wal for 4 yeare i started with 384/128 kbps  and now im on 10000/10000 kbps on fiber optic (sorry for my english).
I use captive portal with limitation(1600/256) and everybody is happy: some play online games with no lag, a few with p2p all time and a rest of as normal user(about 20 user) .
Now my problem with new optical fiber i have acces to metro speed about 60-70mbps, how to get to work this 2 diferent speed 10Mb external and 70 Mb metropolitan.
In captive portal is there any hope? or in other way? please somebody illuminate me to make things in this way:
18 ip with 1600/256 kbps external
                 70 mb metro
2 ip  with 10 mb external
                 70 mb metro
and i wish some how every user to preserve low lag on c-strike and adther online games with all heavy downolad on metro speed (everything to work smoothness).
my best regards in advance.