at least for gnuplot, i've found (part?) of the problem:
  in plot.h, VERYLARGE is defined as HUGE (ie DBL_MAX) 
   i changed line 150 to 
     #define VERYLARGE FLT_MAX
and gnuplot runs fine in X now.
 others report defining floats as doubles also works
  
NOW, someone who know what they're doing, Whats causing this?
does the software emulation define all floats as doubles, hence
what runs on a pc without a coprocessor may break with on 
a pc with a math chip?