r.surf.contour

Hi!
  I'm a GRASS user from University of Cordoba (Spain). I'm working in the integration of a model about land evaluation for the land register of Spain. The
main map I need to elaborate the model is a slope map. The studing zone has an area around 16.000 Has, but is a very narrow feature, and has a large amount of zero values in the current region.
  So, when I'm trying to create a DEM from de contour lines map, the r.surf.contour command starts to works and display: 0%. After 10 hours, the display always is the same: 0%. I know that the CPU of my IPX was working (100%) for all of this time.
  I've worked with r.surf.idw, and I have results, but I need an interpolation between contour lines, not between points in a map.
  Could anybody help me?
                               
                                       Thanks in advance:

                                 F. Javier Almagro Espejo.