have anyone been using gnuplot for the n800? i found it not very user friendly for someone who is not used to linux. can someone guide me to plotting simple functions like linear equations? similarly, does someone know other graphing programs for the n800, preferably one that has an interface?

As far as I know, the only N770/N800 platform app which uses gnuplot is octave. Octave is quite large (being an attempt to imitate Matlab), so it takes a while to learn. Certainly, though, you should be able to do decent plots of linear equations with the octave/gnuplot combination.