I own a Macbook Pro and have an Apple Remote, but I've always wondered if one can use a different remote to control the Mac (like my TV remote for example). Is there an app that could do that?
It should be possible to do so with a universal remote that supports it, but not all of them will. In particular, it looks like Logitech Harmony remotes should work ... check with your remote's manufacturer to find out.
I don't know of an app to 'adapt' to other remotes that don't understand the Mac remote control codes. It's possible that the Mac IR port will only 'see' the signals that it recognizes.