www.xbox-scene.com go to the tut link.
That site works wonders for just about any question you have. Plus as a heads up, search the forums for this because I'm pretty sure it's in here many times. The best thing you can do is read what's already taken place, what's worked for people and what hasn't. Learn from their mistakes.
I see that you have the X3 chip so to anwser part of your question, yes it is pretty freaking easy to install another hdd. Good luck with your mods, and you will be pleased with the results.