Thanks for the advice,

I have a high efficiency furnace with a fresh air intake vent into the
room (ventillation should be OK). There is also a floor drain near the
furnace for water probelms. I will check my furnace documentatuion for
minimum clearance. I am leaving a large area (more than 8 feet) in
front of the furnace for sevicing and I will install a large door to
this area to permit removal of equiptment some day.

Sounds like it will be sufficient to run the top plate up to the side
of the duct, stud on both sides of it, and continue the top plate after
the duct.

Mikepier, you mention screwing the frame. Is it better to nail or to
screw the wall together?

-Sean