I would suggest creating an ARP (Access Role Profile) and attaching it to the "Other" SSID and including a policy list in the ARP. You can find a video in the "Live" section of Spacewalkers which can give you an idea about ARP (also known as UNP: User Network Profile).
In the policy list, you will need to include, not only access to the specific server IP but also every other pre-requisite such as ARP (Address Resolution Protocol), DHCP, DNS as well as traffic going in and out to the Internet. I don't know whether you simply have a router doing NAT/PAT out to the internet or use a proxy etc. If you have a router, you could create a policy allowing traffic to/from the router's MAC. If using a proxy, you can do it with the IP address of the proxy.