What type of ventilation is required when mounting a flat panel plasma
wihtin a recessed wall?  We are mounting several flat panels within 
walls where a soffit has been created so the flat panel will be flush
with the wall.  I know the flat
panel creates heat and since the flat panel will be recessed in the
wall, do I need some type of ventialltion cavity behind the wall,
below, above or around the soffit that has been created wihtin the
wall?

There is no universl answer.  All manufacturers provide specification
sheets and "shop drawings" that detail istallation requirements.

Failure of the panel is likely in hours if the heat is trapped on 5 of
the 6 sides of the panel. If there is an inch clearance all around
plus some extra at the top and bottom, you can install perhaps a one
by ten inch air vent just above the top AND just below the bottom of
the panel. Test to be sure air is entering at the bottom and air is
exiting at the top vent in the second hour the panel is operating. If
the air is not circulating, or the air exiting the top vent is more
than 18 degrees f = 10 degrees c warmer than the room temperature, you
need to get better circulation. Fans of the type used to cool the CPU
in a computer, or similar small fans may be needed to teplace either
the top or bottom vent. Blow air into the space at the bottom or suck
air out of the space at the top. You can run as many as 4 of these
fans on a 9 volt power cube about 4 cm on a side. Use a 4.5 volt power
cube about the same size if the fans are designed for 5 volts instead
of 12 volts.
 However you do it, remove the panel after about two hours of
operation and feel for hot spots on the panel that may need better
cooling. Warm is normal. If any place on the panel is uncomfortably
hot to the touch you still don't have good enough ventalation to that
spot. Your warentee may be void if you have a heat damage failure.  
Neil

If the mfg. provided specifications I would not be asking the
question.  No mfg. was willing to provide information for it is not
considered a standard installation.