The easiest way I have found to adjust the FOV in Black Ops is to bind it to a key in the config file. This is because certain parts of the game, especially the teleporter in zombie mode, often resets your FOV to the default, and it's very easy to then just hit the hotkey and change it again.

In your config file, which is in the players folder in your Steam/steamapps/common/call of duty black ops/player folder (or in the base game folder/player, if you aren't using Steam), add the following string on its own line somewhere in the binding section...

By following this guide, you will be able to survive nearly indefinitely on the "Kino der Toten" zombie level in Call of Duty Black Ops. It may take a few tries to get through the early part of the game, but once you make it through round 15 it will be smooth sailing, until you die out of boredom or simply quit...