Cisco Pix-506E - how to map IPs to inside workstation??

Hello i am a beginner on firewall configurations.
The 506e i am using has already configured for normal operations, that means every workstations could connect to net from it. But i wanna host 3 domains on 1 of the servers, so how can i map those IPs to the server? Or did i have anything wrong on networking concept??

Here are my network design in text form:

ISP router (did nothing) -> firewall (506e) -> switches -> workstations / Server

Please give me a help i've been looking for a config manual for few days but get no result

Dear MaggieKing,

For access from the outside (or the internet) to your inside network you need to specify a static NAT on your firewall and you need to specify an access list to allow the traffic on the specific port. For the basics of PIX firewall config please go through the following URL;
www.netcraftsmen.net/welcher/papers/pix01.html
It is quite simple and useful,

hope this helps.

I'm a noob to this too and am having a similar problem. I followed the link but I guess my problem might be related to using the GUI instead of the CLI. I can get all the users behind the firewall to the internet but as soon as I try and add a nat to pull smtp traffic to my mail server its becomes the only node behind the firewall with access? I've also been told that I can use my Active Directory security in conjuction with the VPN on the PIX but I can't find anywhere to do this. Please ealp!