I also looked a little more into your need to filter the file list, and according to one site, zenity can do this with the following syntax:
Code:
zenity --file-selection --file-filter "*.txt"
(..I haven't tested, as I'm at work on a windoze box )
Yes I have used the Zenity file filter previously and it works well.
I was not previously aware that I could easily call the Zenity files selector from within GtkDialog until musonio mentioned it in an earlier post.
So that seems to solve that 'problem'.
The biggest difficulty I seem to be having is getting the info about GtkDialog into some semblence of order so that I can learn about it in a logical manner.

I did find the script last night that I was going to post for you, but it has a few issues related to syntax changes in recent bash versions.. I should have time to finish updating it tonight and I will post the link when it is fixed.
Thank you. I guess the more examples I can access the more likely I will see most of what is available.
There seems to be nothing to get a new user 'into the groove' - explaining how things are and should be done with GtkDialog.
For instance I still have not come across a definitive list of 'tags' (<label></label>) anywhere with explanations of their uses and options.
The best I seem to be able to do is to look to examples and try to remember what is used and where.
Maybe it is just my head is not in the right place this week and things will be a little better next week

I think I will take a couple of days break from the subject and try a fresh approach next week ...... at present I am only frustrating myself.
***
I have received great tips and examples here and on the pages linked to; but where is the manual that gets you started and then helps you advance with the subject? I seem to have missed it ..... or am not recognising it.
Of the questions I started out with, two have been answered and two remain unanswered.
The Window width and the file selection questions I think are probably OK now.
Why my script threq a hissey when I tried to select a 0Byte file is unknown to me, and I am still searching for a list of <tags>.
Thanks for all the help guys.
Much appreciated.
regards.