hm thats a tricky one.. im still just a newbie and im not that experienced with Nurbs just yet...
First of all. Nurbs do not have faces, its a polygon thing.. the "face" you have selected in your picture is a surface patch wich is a completely different thing. I honestly dont know the difference, so i cant explain it for you.. i might read up on it though.. i could be in the same situation one day hehe
Now on to your problem:
I would think you'd have to detach along the isoparms surrounding the surfacepatch, delete the surface patch and then attach back together, but there could be other ways to do it.
hope i helped just a bit
oh btw.. could you please post images in jpg or gif format. my browser cant show bmp images and besides they tend to be quite big filesize (yours where trimmed well though)
good luck on your modelling