Heyyo,
I'm not sure if BF2 supports IPX/SPX man, I know definately TCP/IP.
Ok, first off, all 3 computers need to have "offline" accounts created. THis means you can play with bots or LAN (possible with bots). Online is for internet (possible with bots), bots, or lan (also possible with bots).
Now, if you wanna use bots, you can. Just get the IP of the host computer, then get the host computer to start a singleplayer map with bots (you can configure the bot count btw, edit the "default.ai" file at mods\bf2\ai\ or somethign like that.. read what it says, it's pretty easy to understand), then once the game's up and the bot's are running around, get your buds to go "multiplayer" and "connect by ip" and there ya go. This method also works for internet too. just connect by ip.
Sadly, the bots only support 16 player maps, but with only 3 of you guys or so gaming this should be fine. I'm sure inna month or 2 once they release the map editor we'll see people make the 32 and 64 player maps compatible with bots (which means add waypoints cause I bet they don't have any right now which's why it crashes with bots if you try).