Stop by my site and check out the guides section for the MOH port guide
or use this link:
http://www.mohadmin.com/nuke/modules.ph ... age&pid=13
You have two options. place the server in your router's DMZ. This will open that computer up to the Internet or forward the correct ports listed in the guide mentioned above.
Make sure your router has the latest firmware. you may want to check out a message board like dslreports for info regarding specific routers and their capabilities.
It can be done. The only problem you will encounter with one IP, two or more computers and a router is, hosting a MOH server on one box. Playing MOH on another.
It could be done but now you have to expose your server in the DMZ.
Good luck and for more info on serving and administrating MOH check out
http://www.MOHadmin.com