yeah that seems good but my case is horrible for air movement and has 1 fan. If the card generates a lot of heat it will shut down my computer. Does the 4850 do that?
Your case should have 2 fans, 1 upper 120mm and 1 lower 92mm both intakes.
Taking care of the extra heat generated by a video card is actually pretty simple, add an exhaust fan, or two, to the case back.