try this:
http://www.kaillera.com/
it needs some work to be ok with Winuae and as i've never really tested it to success, i cannot help. there are members here that do use it to play sensible soccer and other games, so maybe they can help you better. as for the "same team" thing you would like i guess that is completely dependent on the game code and not to a client/server setting, and i don't think Kick Off can be played that way, you can match against your friend tough