Check the in game TAB menus (hit the tab key after loading a game). I swear it was in there, at least in the old versions of mame32k. Obviously you need to be the host player and not be a dick about it, or it'll cause a lot more problems for everyone concerned!
Set your mojob mame color in display to match your stupid ass desktop color to avoid black screen in netplay, fukaz. t(';'t -TFR, AD 2-20-02