pstricks-add redefines a lot of the pstricks macros and uses the extended 
version of the keyval package. So be sure that you 
- load pstricks-add at last pstricks related package
- have installed xkeyval with the special pst-xkey
  (CTAN: tex-archive/macros/latex/contrib/xkeyval/)
- do not load another package after pst-3dplot, which loads
  the old keyval.sty or pst-key.tex

pstricks-add collects a lot of the code which was posted
to the pstricks mailing list and has some more new features:

- pstricks
   o braces as node connection/linestyle
   o line style bar
   o arrows, arrows, arrows, ...

- pst-plot
   o new environment psgraph
   o new macro pstScalePoints
   o new option for logarithmic axes
   o new macro and options for ticklines
   o new plot option bar and option barwidth
   o new options step, start end for plotting data files
   o new options xLabel, yLabel
   o new option plotNo for multiple data files x y1 y2 y3 ...
   o new macro \psplotPolynomial[coeff=<0 a1 a2 ...>]{<xStart>}{<xEnd>}

- pst-node
   o bugfixes 
   o new macro nclineII for a two-colored line
   o new option lineAngle for ncdiag
   o new macros for interpolation nodes
     and linear combination of two vectors
   o new macro ncbarr (line with 5 segments)


pst-eqdf.pro:         the prolog file for pstricks-add
pstricks-add-doc.ltx: the main doc file
pstricks-add-doc.tex: the included doc file

Save the files pstricks-add.sty|tex and pst-eqdf.pro in the TeX tree, 
where the pst-eqdf.pro file should go in texmf/dvips/pstricks/, then 
run texhash or mktexlsr to update the TeX file base.
The document needs the data files in example/.