WD external/portable hard drive for mac -- difference and system/os compat

I'm looking at getting an external/portable drive for my imac and mb pro. What's the different between the two? I saw Western Digital has a my book and my passport, both with usb 2.0 and firwire 800. The passport is only 30 bucks more than the my book. Any experience with these out there? I personally like them. Can anyone tell me if the passport will work with snow leopard and above? The wal-mart site sad it would work with 10.4 and 10.5, but I don't know if that's the minimum or the maximum. I like the passport because it's smaller, and I'm guessing it's built to be travelled with. I have Snow Leopard right now, but am looking to move up soon, I think, once I know if Java 7 is ready for Mountan Lion yet.

The MyBook is what they call a Desktop External whereas the Passport is a portable external. The main difference is size and power. The Passport can be powered just from the USB drive - so you don't have to carry around a power supply as well. If you are going to use it at a desk then price may matter more than size and power supply.

I have both Passports and Mybooks and both work. The Mybooks are connected to my Computer that I use as a Media server - so I don't really move them around. The Passports I use for my Laptops.

Oracle Java 7 does work on Mountain Lion (Except for Chrome because Chrome is 32 bit) That being said - some Cisco applications I couldn't get to work with Java 7.

So I assume, IvanLaston, that the passport will work with Snow Leopard and above? If so, then i think I may exchange it for the passport. I like the smaller size, I think. Although, reading your reply again I was wondering if I'd need an external power supply to use the firewire, or no?

Either will work. I have a My Passport on the way but it's stuck in NJ at the moment

External hard drives work with just about any OS out there. The passports I have - have worked since my first Snow Leopard machine. They worked on lion and are working on Mountain Lion.

Every Passport I have seen does not need external power no matter the interface.