I'm not a psychiatrist, but here's a stab at an answer...A psychopath suffers from no specific mental disorder but shows a pathological degree of emotional instability. He/she is unable to form personal relationships and is ignorant of social obligations. As a result, violence, sexual perversions etc are common with them.
A psychotic does have a serious mental disorder - often suffering from delusions, hallucinations etc - and has no insight into his/her condition.