Controling the width of a progress bar

ok i have a project where i am clicking thou a 12 image slide presentation, the button loads xml feed image, and xml controlled text. my question is at the bottom i want a progress bar. every time i click i want the bar to fill up a tad. and i want it to be scalable. where if the slides turn into 13 or 20 i can just adjust maybe a few arrays to adjust but i dont know where to get started can someone help?

:crying:
any help is great/

Thank you