configure cisco router NAT dynamic & static

I have a Cisco 831 router that works fine for getting my LAN onto the internet via my cable internet connection. It runs cisco software 12.3 I started setting it up via Hyperterminal/console cable and Cisco SDM 2.3. It seems to be setup for dynamic NAT (I think) so far, but I need help getting Static NAT setup. Since I have several static IP's from my ISP and I want one public IP to point to the private IP of my email server, and another public IP to point to a different private IP that runs my web server. I'm at the stage where I hook up the Cisco 831 and it gets my LAN on the internet, but I had tried adding some static NAT entries, and the computers on my LAN that I had made static entries get a error sorta like "there is another device on the network with this ip" when the cisco 831 is on. Maybe I could send you my 'running-config' and you could tell me from what I have so far what I need, what I don't need. Thanks