You can turn on the constantly computing impact point, either offline, in H2H (if you are the host), or I think it works in the Training Arena (maybe not).
To do so, open up the clipboard and press setup, then arena settings, look for the parameter "FlightModeFlags". Click on that, select the change button, and look for "dive bomb sight". Turn that on and press ok to exit the setup. You see, whenever you have a bomb selected that there is a little + sign on the ground which tells you where the bomb would hit if you dropped it that instant. This'll help you get a feel for aim points when you are diving.
You can also use this same sight to practice calibration in the bombsite, but that's covered in a number of threads in the help, so just search for one.
Don't get too reliant on the dive-bomb sight though, it doesn't work in the MA.
-Soda
The Assassins.