matt, I think aogor ment that the curve he has to begin with isn't planar.
And yes aogor, there is. Unfortunately, you're going to have to divide the curve into four segments to get it to work.
aargh. I can't remember the exact command (and this computer doesn't have Maya). But the tool you'll need is under 'surfaces' in the modeling menu (I think). Basically, pick two opposite curves of the four you have, then the other two (order doesn't otherwise matter), and maya will fill in the surface.
So, say your curve went from a straight line at the front, to a half-circle at the back, with the two sides simple straight lines (the half-circle stands 'up' out of the plane). The surface would start out flat at the front, then gradually morph to a curve over the distance, all the while keeping the ends of the curve down at the straight lines of the sides.
Although another way to do this is to loft the surface you need, by creating cross-sections of the desired curve....