If you've installed the Community Pack, your net rates have already been adjusted, but if you wish to further adjust them to match a very high speed connection, follow these steps. Of course, I recommend backing up any files before you modify them.
Open your Nerf System directory (usually C:\Program-Files\Atari\Nerf\System) and locate a file named Nerf.ini. It will look like a notepad with a gear on it, and the extension may not be visible by default on all operating systems. Open this ini file and look for a line that reads:
ConfiguredInternetSpeed=<SOME NUMBER HERE>
By default this is set to 2600, with CP, it should be 10000. For a higher speed internet you can set this number even higher and this will allow more data transfer between your PC and a server. It's like widening a freeway from 3 lanes to 6, you get more cars (data) that can travel the freeway (connection) with less congestion (lag). But remember, your game can lag if the number is too high also, so don't go too high. It is best to test your settings before and after to see if any difference its noticeable.
If you plan to host a server you also need to find this line:
MaxClientRate=<SOME NUMBER HERE>
Also set this to 10000 or higher, this will mean that a client on your server will receive a maximum of 10 KB per second while on your server. This should be very helpful for running large maps or complex mutator combinations.