how to update window content?

["sahlot arvind" <asahlot gmail com>]

Hello all
I want to write a program in which i click on a button and user can see
a string moving from from left to right like marquee in HTML.... for
that in call back to the button i m using sleep () function and i am
drawing string again after sleep () at a different location but thats
not being updated i mean i am not getting anything like marquee rather
i am getting just last content updated string ....so is there any way
to update screen content??? some function for that... like we have one
in java repaint ()....
its urgent...
Thanks and Regards