Access the internet from an other domain

i have a branch of our main office.main office gives us the facility through Radio modam of internet.the ip scheme in main office is 16 bit,at the moment my systems are connected to the main office through DHCP.and we are using the internet but connecting to there DHCP.

but now i want to set my own domain here in the branch office.and just want to use the facility of internet form main office.i want to use 24 bit address in my office.
so please help me to this job.i just want to use the internet facility but establish my own network.