You need an "import os" (or "import os.path") in commandinterpreter.py or running GPL() doesn't work on windows (because you use os.path to open COPYING). Porting to other platforms really is good for finding bugs... Also, it comes out in a narrow column instead of wrapping nicely, and it has a few error characters in it which are probably from unix EOLs. I've expressed it all in a nice picture!
http://www-xray.ast.cam.ac.uk/~jc/veusz2.jpg (apologies for the crappy .jpg format) Jamie
