Oh bugger - the well used ignition parts are the usual suspects.
If you've changed the spark plugs, HT leads, rotor arm and dizzy cap - it may be your fuel - you said you just got the car - have you filled teh car up since? - there is a small chance previous owner put really cheap petrol that the car does not like. Otherwise I think it's time to take it to the garage and get them to sort it out properly.:S