I'm buying a new computer and one of my friends wants to buy my current one from me. Neither of us have ANY idea what it's worth. It's a Compaq Presario with nothing exciting on it, 2 years old, and the uh, important numbers are 512MB, 80GB, and 2.5GHz, whatever the hell that means. I have a flat screen monitor and speakers. I don't really remember, but I probably paid around $800. Any idea how much I should charge? Thanks.