Is there a way to trick the Android Market into thinking I'm using a different device do I can download protected apps? I have an unrooted Archos 70IT with the market add-on app and there's a number of apps that I can find in the Market on my Droid but not on my Archos.  They are likely "protected apps" which can only be installed on devices approved by the apps dev. 

To get around this I just download them to my Droid, save to Dropbox then install on my Archos.  These apps work just fine, so rather than be "protected" from "incompatible" apps and having to do backflips to get the apps I want, I'd like to trick the Market into thinking I'm on a Droid or some other ubiquitous Android device.

Is there anyway of doing this a) at all, and b) on an unrooted device?  If so, how?
Yes, it can be done but it requires root.  You edit the device fingerprint in the build.prop file.  Here are details: http://androidforums.com/samsung-galaxy-spica/98024-protected-app-market-fix-tutorial-build-prop.html

Edit: For a more complete answer, see How can I modify the phone model in build.prop to get unsupported apps?