Of course its possible, but we must have more details about your question. There is modems-routers with Multi-NAT service inside. Multiple public IP addresses can be used (static or dynamic) on Internet. You didnt specify do you mean on Public or intranet side. Public addresses range must be given by ISP, and intranet or private is based on sysadmin management. Sysadmin can manage router and make policy about usage of IP address resources. Often companies dont have only one public IP address, in some cases company leases pool of 5-15 public addresses, for various purposes, as dedicated mail server, web, VPN,... Modem/router can use several of them, not just one IP address, of course this depends also from modem/router capabilities, he must have that capability to support that.is it possible that two PC's connected with same modem have different ip address...?
if yes then how to change their ip address??