Yes, it's possible, but the resolution is limited to 1024x768.
Also, you can only mirror the internal display, not extend it. There is a firmware hack that allows you to extend the desktop, but it voids your warranty.
As far as that mentioned hack is concerned, you can find info and feedback on it @macosxhints.com(too lazy to post link, sorry). It will void your warranty, but if you need screen real estate...