Whoops I'm sorry: I'm using Perl\Tk. And the reason why I need this tabulation is to create two columns in the listbox. Now I'm aware that HListbox can do that easily, however I need to precisely and exclusively control all the keyboard-arrows bindings, and HListbox comes with pre-packaged bindings that I would have to fight all the way. Also, I'm aware of the possibility to command two listboxes at the same time, but I don't want the separation in the middle. In other words, I'm pretty happy with my simple Listbox, but I need to be able to translate this "unprintable character" into a "real spaced" tabulation... Hope that clears up some confusion.
As far as I know this is not possible, the list box will strip out any special characters you pass to it. You can get a column layout with spaces; however this will not be a true tab. You will also need to apply a variable number of spaces in-between the strings to get the columns to line up properly.