networking

hello guys i have 8 computers connected to each other wirelessly using the linksys wireless G adapters through a linksys router B model as a local network they share files and printers. Now i want to add internet connection to the router but when i add it automatically the 8 computers will go online since they r connected to the router so what i need is to restrict 6 computers from connecting online and let 2 computers only access the internet and still be able to communicate with the other 6 computers wirelessly through the router as a local network