I think this would be a help with my experienced with Linksys router (a basic one also)
You only need one NIC card to access internal IP and external IP. The trick was in the router.
Just set your router in DHCP mode then reserve a private IP address like 192.168.1.254 and of course I assume that your default gateway would be 192.168.1.1 and subnet mask of 255.255.255.0
Configure this in your server by "yast lan". Test everything from workstation to your server. If it is good, don't touch anything. The next trick is in your router to get your external public Ip address.
How to do it?
Simply -- add your private IP address of your server (192.168.1.254) in DMZ tab. Then save setting, you are good to go!
To find your public ip address just go to your one of your workstation stations, open a browser type
http://ipchicken.com/. This will give you your external public IP address.
You can test it if you want to access your server just open another browser and type the public ip address. then you will see your vicidial welcome page.
With regards with your station sure you can have an internet access (remember your set your router in DHCP?) just set your workstation IP address acquire automatically. Happy surfing!