From what I've read over at XDA-Developers, it can't be done without root. Something about the need to read from a file in /dev/graphics that can't be accessed without root.
If it were possible, I'm sure there'd already be 100 different apps out there. It's not a problem with the Droid, it's Android from it's first iteration up to 2.1.
Yea, I don't think there's a way of reliably grabbing the screen without rooting. What's wrong with installing the Android SDK and using eclipse to grab screenshots? Its not that hard to setup the development environment, and once you have it installed you can play around with making your own Android apps