Axe, there's a really great book by Tom Kolb called Modes for Guitar that I'd recommend. He gives a simple explanation of what modes are, and then describes each mode and how its often used. The book comes with a really helpful CD that has riffs to give you ideas for using modes, along with a backing track for each mode. I think one of the most important things to understand is that using modes involves a lot of ear training. Its when you start playing different modes over appropriate chords that you really hear the distinct quality of each mode, and start developing a feel for how they sound. So make sure you have a good, easy-to-use playback system to practice with. It also helps a lot if you already know how to play the major scale across the entire fretboard in different keys, because as Caponi has already suggested, you can use those same patterns when playing modes (something Kolb explains clearly in the book).

Good luck!