How to modify create your account fields?

[AudioPro]

I'd like to find out how to modify the create new user account section such that about 2/3 of fields are stripped out.

I've done some site testing with a fair number of friends and long time clients and what we've arrived at is that must people when creating accounts only want name email password and the "required" fields should be much more clearly defined. This page alone will cost me approximately 15% in potential registered clients and as such needs a major overhaul. So in short, what files need to be worked on and generally what would I need to do?

-Carl