iTunes library on external drive - how to format internal HDD and lose nothing

I'm just about to format my main HDD and reinstall OS X. I'm looking for a quick answer to an iTunes question.

I have my iTunes library on an external HDD. I have backed-up the "iTunes Library" and "iTunes Music Library.xml" files from the music folder on my main HDD. Once I have reinstalled OS X how do I get my iTunes working again.

As I said, a quick answer would be much appreciated.

Steve