OS X is based off of BSD as I understand it, a big departure from the previous Mac OS's. MsMittens is right, setting up a dual boot system is your best bet. My reccomendation would probably be SuSE Linux. It comes with an NTFS resizer to aid in installation. Reading is going to be the best help you can get with this. Read a book, and try out what you read on SuSE.

I'll add an interesting book to the list though...

Universal Command Guide

It's an incredible book that covers just about every Unix, Linux, BSD, Windows, and Mac command. Oh yeah it has Netware stuff too. It's a good way to learn your way around systems because it shows equivalent commands in the various OS's.