1. install ipx (same settings on all computers)
2. DON'T run carma 2 with carma2.exe
Use for it dirrectly carma2_hw.exe (with 3dfx emulator for 3dfx mode or create shortcut to carma2_hw.exe file and add "-d3d" parameter to start in Direct3d mode)

u need run game with this way at both PC. Then try LAN game.

If you use alt+f4 to quit game, process (carma2_hw.exe) didn't unload from memory, so you need to kill it with ctrl+alt+del and then start carma 2 to LAN game can work.

But lan game is bugged sometimes, i don't know dependances of it.
Sometimes it run fine, sometimes game crash or something else.

For game by Internet i use OpenVPN (need to use "dev tap" in config file).

Tested with 2 PCs connected by wire LAN. Both WinXP SP3 32bit with RU, UK and US versions of carmageddon. Just use same releases/patches/mods.

And sorry for my English... it isn't my native language.