thx for the answer.... i did fill the channels manualy on myth-setup, and they work (without scanning). What is making me crazy is the bottom colored stripe (changing colors like a rainbow).
Regrading the grabber, there is no grabber for open-air tv in Brazil.... that's why i've try us-bcast and us-cable, because their frequences are the same in Brazil. But this is my minor problem...
The main problem is the rainbow stripe.