That's just a coincidence. Normally people only see the nie- prefix, but even this isn't really a prefix here.
@GIJoeski, you are on the right track. "Nie" is negation, "na"- (a one of the meanings) was used in Old Slavic language as a prefix to reflect completeness of the action with a touch of fullness, sufficiency. From Old Slavic -навидѣти- to see with pleasure. So, "nienawidzić" - "ненавидѣти": не (nie) negation, на (na) fullness, видѣти (widzić) to see.
Не-на-видѣти -- nie-na-widzić -- opposite "to see with pleasure" -- hate.
GIJoeski, your analytic scills are good ;-) Good luck in studying!