Landlord violation of lease???

im facing two issues here, I live in Fort Kent Maine, I prepaid my rent from August 12th 2008 untill November 30th 2008my lease is month to month and also states that the landlord must give at least 24 hour notice when entering or showing my apartment, the building is for sale, and so far on two seperate occasions that I know of he has sent people over to my apartment, without escorting them, with a key for my door, also without notifying me at all. I want my prepaid money back, we wont give it back. Also I do not smoke and have a newborn baby but nieghbors do smoke and my apartment smells like cigarette smoke all the time. What can be done about this???

Unless he guaranteed you a no smoking building, nothing can be done about the neighbor's smoking. Smoking is (as of now) still legal and the LL cannot curtail it unless he does so by lease or rule. If he didn't specifiy no smoking at move in, any party is free to smoke in their units or patios.

As for the entry problem, cite the state law (ME Revised Statute Title 14 section 6025) which states that he must give you 24 hours notice of entry before making such an entry. Let him know that you will pursue legal action (an injunction against further entry) if he fails to follow the state law. Send this notice to him certified, rrr, and keep a copy.