Create a game as u normally would, but before creating it, you need to go edit preferences and make sure the box named "run as server" is ticked! Then once the game's created hand out u're I.P. You can find that by going to game status.
Opening ports on your Windows XP firewall
1. Navigate to My network places
2. Right click your internet connection(for example, LAN- connection 1). Select Properties.
3. Click the 'advanced' tab, select settings.
4. Select the 'services' tab.
5. Click the 'add' button, in the lower left corner.
6. Enter a description of the program(CM), type your ip number, and enter 9094 in both the external and the internal port number boxes, make sure the TCP box is ticked.
7. Repeat 6, but now enter 9093 in the external and internal port number boxes, make sure the UDP box is ticked. Now click the 'ok' button.
8. Make sure both new created services(CM) are ticked in the 'services tab'. Now click ok.