ADSL TCP/IP PROBLEM

I recently ordered an ADSL service and I was given 5 IP addresses, one network IP, a default gateway and a subnet mask (that allows only the 5 IPs of course). I have 15 computers on the network, 13 of them are running win98, one is running winnt wksand the last is the winnt pdc. I need to allow all the computers to access the internet through the adsl router using only one IP address. Can anyone help?