tkinter dialog box

[Ajay]

hi!

i need to write a dialog box that asks a user for a username when the
application starts up and another dialog box that asks the makes the user
choose a file and build a user model.

the way i want the dialog box is that the user should be unable to proceed
with the application until they complete the operation in the dialog box,
something like a JavaScript prompt. any ideas of how to go about designing
something like that.

thanks

cheers