Double click battle.net gateways. You should see something like this:
1001
02
uswest.battle.net
8
U.S. West
useast.battle.net
6
U.S. East
asia.battle.net
-9
Asia
europe.battle.net
-1
Europe
NOTE: If your gateway list is already screwed up, simply delete all the text you see here, and hit ok. Now next time you go to the battle.net screen, the four default battle.net gateways will appear again. The format for adding a gateway is as follows:
Server address
Time zone
Server name
So let's say you wanted to add Bnet-X to your server list, you would just add this to the bottom:
bnetx.pgtour.net
-5
Bnet-X
So your Battle.net gateways string would now look like:
1001
02
uswest.battle.net
8
U.S. West
useast.battle.net
6
U.S. East
asia.battle.net
-9
Asia
europe.battle.net
-1
Europe
bnetx.pgtour.net
-5
Bnet-X
Just hit OK and you're done!