Sins of a Solar Empire is UNPLAYABLE as a multiplayer.
darkcurrent,
Unplayable how? You can't host? Your game crashes? You're experiencing lag? It's quite difficult to provide support when there is no further information given.
However, I will try anyway...
If you're running game version 1.05:1. Disable/uninstall all MODS while troubleshooting.
2. Please make sure your OS, and all device drivers are up-to-date. Sometimes it helps to un-install old drivers (and actually un-install the device in the device manager, then re-boot) and then install the new drivers.
3. If it's hosting issues you're running into please download and follow the instructions in my guide linked-to under the GREEN writing in the OP of
this thread4. If you suspect latency, first run a ping-test to your local gateway if you want to take your ISP out of the equation. You could pipe the ping-test to a textfile to e-mail to your ISP support if it shows issues (I find doing so, helps convincing some ISP's in sending out a tech to make the corrections

)
If the ping-test to your ISP's local gateway is fine, you could run a "trace" (tracert) to ICO's IP if you keep getting disconnected from ICO (you can find ICO's IP by running "netstat -a" while in-game and connected to ICO)
or run the "trace" to the IP of a friend you're trying to play the MP game with if it's the friend you're having higher latency to.
If you're running game version 1.1 BETA (v1.09):1. Disable/uninstall all MODS while troubleshooting.
2. Please make sure your OS, and all device drivers are up-to-date. Sometimes it helps to un-install old drivers (and actually un-install the device in the device manager, then re-boot) and then install the new drivers.
3. You should not be having any issues hosting with the new netcode (Alloy) in the 1.1 BETA version. I've tested it with many firewall/router configs and Alloy "tunnels" past/through them all with ease.

4. **same as for version 1.05**
Please post back with more information so we can be of more help...
thanks,
the Monk