was it the gearbox or engine that siezed?
if engine could be headgasket gone, or timing belt, you will need a mechanic to look at it, as it could really be one of many causes. same if g/box siezed, you will need it to be looked at, but engines & auto boxes are expensive to fix, you might need to consider going to a good scrappy for replacements as this can work-out cheaper than engine/g/box re-builds. ask different garages to get best price. Good Luck.
hope it helps, August 2010