Andy: many thanks. Worked second time, because the tkinter install also needed to access the Debian archive on their site, and as the Pi was not connected to my router first time round, it failed. Second time, with the ethernet cable in place it all seemed to work, accessing an additional 4.5MB from archive.
However: when I ran my software, the start up text appeared as expected in the terminal, but when the program attempted to create the GUI widgets (frame, canvas, text box and a number of buttons), it crashed with:
Traceback (most recent call last):
File "GUI.py", line 670, in <module> app = Application()
File "GUI.py", line 233, in __init__
File "/usr/lib/python2.6/lib-tk/Tkinter.py", line1926 in __init__
BaseWidget._setup(self, master, cnf)
File "/usr/lib/python2.6/lib-tk/Tkinter.py", line1901 in _setup
_default_root = Tk()
File "/usr/lib/python2.6/lib-tk/Tkinter.py", line1646 in __init__
self.tk = _tkinter.create(screenName, baseName, className, interactive, wantab???
???cts, useTk, sync, use)
Tkinter.TclError: no display name and no $DISPLAY environment variable
(I captured this with a digital camera shot of the TV screen. the ??? are characters I can't make out!)
Perplexing. I already knew the software ran ok with Puppy linux booted off CD on a laptop, so I decided to check the full Debian 6.0 download by loading its ISO into a VM Player virtual machine. Again I had to install Tkinter (getting good at that now!), and again additional stuff was downloaded from the Debian site, about 4.1 MB . My software ran just fine.
So, is this a problem with the Debian SD card image for the Pi?
Anyone else out there with any thoughts?