Quote from Hombre:
What are the visa requierements for a long term stay of 4-8 months ?For US subjects.
http://bangkok.usembassy.gov/service/thai-visas-for-americans.html
The above link is the "official" information, but I know that if when you get to Thailand and get a good Thai lawyer then anything is possible. The Thai lawyers know the ins and outs of the system and have connections. So if you want to stay for an extended period of time without Visa issues then you might be able to...
My advice would be to hang around a bar/hotel, like the Secrets, and talk with the owner there. I believe he is available on the message boards. An American who owns a business and lives there can give you the skinny on avoiding visa issues and may refer you to a good Thai lawyer.