If your looking for a GUI editor, have a look at these:
- wxFormBuilder can generate .XRC files for wxpython.
- XRCed ships with wxpython and could do this as well.
.XRC files are xml file which describes your GUI and are not language specific. You could load these files from a Python 2.6 and a Python 3.0 without any change.
WxPython is currently available only for Python 2.6 though. I would not worry too much about converting a python 2.6 to 3.0. This is the matter of a few lines to change.
The problem with the .XRC approach is that you still need to glue these xml files with Python code. If you're a beginner this might be as tricky as writing the GUI by hand. That's the problem with WxPython anyway: I don't know any real good editor for it, have a look at this discussion