[Xavier]

i'm sure someone around here knows more than i do...but the things that jump to mind are:

are you sure you're entering the server ip and port # right?

are you trying to use an illegal copy of the game, or one purchased from ebay or some other unauthorized reseller? Another way of asking this is if the CD key you're using is printed on the inside cover of a manual that came with a game you purchased from an authorized seller.

other than that the only thing I can think of is router/firewall issues. make sure you're able to send and receive traffic on the port the servers are on.