I have a scenario where my ISP is providng only private IP(192.168.x.x) with a gateway(192.168.x.x) and a dns server(public). I have an internal LAN with IP's in the range 172.16.x.x. Is it possible to configure my ISP's IP address on fa0/0 and my internal IP address on fa0/1 ? Will the clients in the internal netwrok be able to access internet ?
This is certainly possible on the 2811 to translate addresses even when both addresses are in the private address range. In fact for translation it really does not matter whether the address ranges are private or public. Your config might look something like this:
ip nat outside
ip nat inside
access-list 50 permit 172.16.1.0 0.0.0.255
ip nat inside source list 50 interface fast0/0 overload