If you make seperate partitions, it would be very easy it essentially makes it into two seperate drives. Google how to partition a harddrive if you aren't familiar. It's fairly simple.
Will a WD My Book 2TB work with OS 10.4 on a 2005 eMac? For several reasons, I'm milking my older computer dry!! I read that re-formatting for Mac is possible - but will it go back to OS 10.4? Thank you.
My Mac is an '07 (iMac 7,1) with an Intel Core 2 Duo, and it works on mine. I am running OSX10.6.8, so I'm not sure how much this helps you. You could probably get an answer from Apple...