graphs customising

Hi all, 
I have been trying to modify the default look of the graphs generated by xymon without any success. I have tried to play with hobbitgraphs.cfg, changed few things but it sill does not want to generate better looking graphs. 
I have seen many nice graphs generated by RRD but can't make it work with xymon. 
Do anyone knows about any decent tutorial somewhere online? 
Many thanks. 
Oliver