I'm sure I'm just not looking in the right place, but where is the "convert to face" command in XSI?
Scott
Some time ago, I asked me the same 
But I was told that XSI is still far from being finished (which means that the NURBS tools are still incomplete, so the convert to face isn't included yet in XSI 1.5).
I suggest to using Subdivision Surfaces or Polygons instead of NURBS. You also can create the face in Softimage 3D and import it in XSI.
Andillo
www.3dartist.f2s.com
Just draw a polygon instead of using a spline and converting it.... Works for me.