How to setup an external HD for backups

I want to put together an external HD for backing up my two laptops. It will be for photos, documents, etc, but not the OS or programs.

Obviously I need a hd enclosure and hd. But do I need any thing else?
I guess the power supply and fan is already included in the enclosure, right?

So is it a matter of connecting the hd into the enclosure, then connecting it to a pc with a usb cable? Is there anything else to buy or know?

BTW, I'm not a pc power user. I only backup when new content has been added to my hd, which is usually once or twice/week. So if the enclosure is not left on all the time, does it need a fan?

And finally, is the backup utility in Vista and Win 7 good enough incremental data backups, or should I consider something else?

Sorry for so many questions, thanks in advance!