Okay, better step-by-step.
1. Open up server.cfg in the configs folder.
2. Look for the part that says
set oppass1 ""
set oppass1level 1
set oppass2 ""
set oppass2level 50
set oppass3 ""
set oppass3level 100
set oppass4 ""
set oppass4level 150
set oppass5 ""
set oppass5level 150
rcon_password ""
3. On the 'set oppass5 ""' line, insert your password between the two quotes. For testing, make it aaa or something.
4. Save.
5. Make a shortcut of paintball2.
6. Right click it, go to 'Properities'.
7. Where it says 'Target:' add +set dedicated 1 +exec server.cfg +map *mapname*
8. Press okay, and double-click the paintball2 shortcut.
Now, the using of the password.
9. Start up Digital Paintball. Go to Play -> Join Game
10. Join your server.
11. Bring down the console (~) and type 'login *yourpassword*'
You should sucessfully login.