Variable Backgrounds

Hi,
I'm looking at making a new Mac App, and could use some advice as to where to start, and what the easiest method will be.
I would like to make a variable background, that hopefully shows a picture, as usual (Which the user choses), and then adds an effect on top of it.This effect would change, and I'm thinking Quartz will be easiest (?).
However, I'd like it to have an UI, and I'll settle for a Pref Panel, but I'd prefer a fully launch-able app that runs in the background type of thing.
The only thing is, what do I make it in? Is this an Xcode job?
Also, will the constant (Hopefully on loop) Quartz running in the background chew up the CPU/GPU?
Thanks,
Joseph Dufy