I've answer your question briefly in a message on SimuWorld.linkka.com.
Here I can give you more details in order to use gnuplot together with Pizza tools
1. The Windows version gnuplot has two exes, wgnuplot.exe and pgnuplot.exe. You should
use the later one. You can try to put the full path in the DEFAULTS.py or add the path to
your ENV path variable. I did the later and it seems work well (you could try to play with
the forward/backward slash if you want to use full path in the Defaults.py:)).
2. On Windows first try to set the terminal to 'windows' in DEFAULTS.py. As a result, in my
Defaults.py the lines look like
PIZZA_GNUPLOT = "pgnuplot.exe"
PIZZA_GNUTERM = "windows"
3. Do not use the 'complicated' test_gnu.py first. Instead try to put these
line into a *.py file the run it and see if it works.
g = gnu()
g("plot sin(x) with lines")
print "all done ... type CTRL-D to exit Pizza.py"
4. Finally, if you are still stuck. Please try to use Python 2.6.2 and download the
latest version of Pizza tools, because these work well on my computer.