calling a gtk program from a backend cups

I've just written en c tiff cups backend but i need to ask some variables
to perform archiving of this tiff. so i've made a gtk program to ask this 
parameters.
The problem is when i try to launch the gtk program from cups backend using the 
system function of the glibc it doesn"t work and it doesn' t launch the program 
at all can somebody
tell me how i can do this stuff.


Thx a lot
  Serge Sterck