Assuming the car was running fine before this problem started then I'd say it's a flat battery I'm sure. The starter needs to draw an awful lot of power from the battery, if the lights on the dash go out/dim when you try to start the engine the starter motor is getting power.
Before you go replacing anything just borrow some **GOOD** jump leads and I reckon you'll be on your way in no time (trust me - even if you think the battery is fully charged).
Matt
August 2007