How to get Multi-Player working:
Added by XFlak (Thanks for helping)
-If you've already launched the shopping channel on your Wii at least once in the past and already accepted some agreement, then u can skip this step. Install the latest IOS56 and the latest version of the shopping channel. Launch the shopping channel and accept the agreement.
-launch the usb-loader with any cIOS that has base 56 or base 57 (if u don't have one, install it)
-launch the game with a cIOS with base 57 (if u don't have one, install it)
-create 2 campaign profiles, start the campaign with each of them and save and exit
-launch multiplayer with both profiles (obviously the Wii needs to be connected to the internet), it should work on your second attempt (and then the first profile will start working afterwards). You will be prompted to update, say yes. Note that this is an update for the game, it is not an official firmware update and is safe to accept.
When you wish to play COD: Black Ops, choose IOS 250. The game should launch right away, and you will have no more problems with Online, Freezing, etc.