The FCC field notices make for some pretty good reading:
http://www.fcc.gov/eb/FieldNotices/
I have not yet noticed anybody being busted for running a mini-TV station... but there is always a first for everything!
For FM, the limit for an unlicensed transmitter is 250uV/meter at a distance of 3 meters from the antenna (pretty darn weak)... I am not sure what the limit is for the TV bands.
jr