Is your car a 5spd or auto?
probably a rotten hose.
could be a cracked radiator.
Check the coolant and let us know if the color is off.
Also, what type of clamp do you have on it? Is it a worm clamp (use a screw driver to tighten it), or a compression clamp (use a pair of pliers to open it)?
--When rubber heats up and cools off it changes shapes and sizes. As this occurs over time the radiator hose gets "skinnier" and "skinnier." If you have a worm-clamp on the hose shrinks and the clamp stays the same size. If you have a compression clamp it maintains constant pressure on the hose to account for the changing sizes.
(There's an official name for this... like "charged cooling" or something, but I forget what its called..... lol)