isight

Are you already an experienced programmer? If you're just getting started learning to program, have a look at the guides at the top of the programming forum, also do a search using the link in my signature for topics on learning to program on the Mac (there are TONS of threads on this topic already).

You can tap into the iSight, but that is relatively advanced, and you likely won't reach the point where you're writing software that interacts with it for a good while, if you're just learning how to program.

If you're already an experienced programmer, please forgive my assumption to the contrary.

 

What do you plan to do with the camera? Be specific.

Maybe something like the Processing language, which has video-input and video-playback components:
http://processing.org/reference/libraries/video/index.html

Without knowing specifically what you plan to do, it's difficult to offer specific advice.

 

Maybe you don't need any programming at all

Start iChat, focus whatever you want to have in the picture, and press the following keys simultaneously: command shift 4

A small cursor (a circle with a cross) will appear on screen. Move this cursor to the left top corner of the picture you want. Click and keep pressing the mouse until you cover the area for the picture (You'll see a gray transparent rectangle). Stop pressing the mouse and a Screenshot......png file will be in your desktop.

The last part is known as taking a picture of part of the screen.

 

Describe your program. What is it written in? What capture rate do you need?

Your first post implied that you had no Mac programming skill at all, and therefore no program. If you already have a program, you need to describe it.

If you're just looking for general information on how to get live video captures, then look at QTKit (google it). If that isn't what you're looking for, then you will have to provide more detail on exactly what you're trying to do, in what language.