Ok, since you said you're using XP, I'm guessing that one of the PCs is connected directly to the internet (without a router, you said), and then you're using XP's Internet Connection Sharing (ICS) to share the connection out to other PCs via 2 switches. And you're running FSHost on one of the shared machines.
If that's the case, then I believe you'll need to setup port forwarding on the server machine (the one connected directly to the net), and forward certain ports to the machine running FSHost. Otherwise, when people connect, they'll be trying to connect to the server machine, which isn't running FSHost. To do this, go to the server machine, to Control Panel / Network Connections, right-click on the internet connection, select Properties, and change to the Advanced tab. You should see a Settings button in the lower right. If it's grayed out, you'll have to turn on the checkbox at the top for the firewall ("Protect my computer..."), then change the settings, and then turn it back off again afterwards -- the port forwarding you setup under Settings will still be active even tho the firewall is not.
On the Settings page, you'll see a list of ports that are preconfigured. All of them should be unchecked, since you don't need them. Click Add, type something like "FSHost" for the description, put in the internal IP (192.168...) of the machine running FSHost, and set both the External and Internal ports to the same number. Select TCP or UDP, and click OK. You'll need to do this for each of the ports listed on the link that Jon mentioned above. The only problem is that XP's firewall won't let you setup port ranges, and one of the things you need to setup is forwarding for UDP ports 2300-2400. You could probably get away with forwarding just the first 5 ports or so (2300-2304), since it usually uses those ports first (no guarantees). There's also a program called DXport that will limit the number of ports used by a particular PC, and that might help in that situation also. (
www.puffinsoft.com)
I guess I can create a session on the server and join it from my IP, but a server isn't really ment to put games on it.
Well, FSHost isn't a game, it's a server. So putting it on the server really makes perfect sense here :-) I'd go with that option, if it were me.
Russell