IP Chains

Hi I wanted o ask u about a problem regarding my project. The project is related to "Cyber Cafe Authentication". Here we have to chk whether a set of user name & password is valid and if valid allow this user access to internet. All the scripitng has been done in PHP and the operating system is linux. Now we just have to link "IP CHAINS" to our php script. That is when the user is allowed to access internet, ip chains should start running through the script. However we are stuck at this problem & cannot find a sound solution. Can u plz help us? That would be very nice :) Waiting anxiuosly for ur reply..... Regards Faryal