Yup, i guess you do.... B3 client isn't compatable with B4 servers. So.... yea, i guess you can't go to the official test server. I have both servers which i can run easily, and i've generally got the B3 server up on unislash.game-host.org , so you can work with that server. It is updated as far as maps a bit more, but the official is updated to the CVS every time it resets, so it is a bit more updated as far as everything else.

Cheers,
Unislash