I got an Cisco ASA 5505 and have configured it as simple as possible
just for use in a test-network.
I got the IP-address from my provider
The DNS is the one we normaly use (it works in my other router)
The PC I connect to the ASA get's the 10.100.2.x IP-address, the gateway
and the DNS, but no connection to the internet.
Setup is attached.....