Currently, I believe that you can only refuse connections by their initial ping rate when joining a game. I set my initial ping faily low, I haven't had any problems, other than occassionally people pinging out at 999. Sorry I don't have any more info for you.
KILLAH! Hey man! biggrin: Guess you forgot your old password. Where ya been man?
Anyways, basically what Big Ern said; set the maxping at like 600 or 500. You can get RCON commands like that from Rudedog's RCON guide over at http://www.mohadmin.com