I'm building a computer for a friend, but I don't know much about what video editing requires. So, can someone please give me a quick direction on what I Need please?

I have a $800 budget to work with, so what should I get with that? The most importnat is what video card, processor, ram, will do the job. The rest such as the case etc can be quite easy to sqeeze in.

ANY input would be helpful...THANKS