Internet Explorer version 8, Windows XP

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I am using internet explorer version 9 and my Operating Sytem is windows XP. I want to know why is it that everytime i upload a file to a program designed espicifically to internet explorer bversion 8 the file won't upload and the dialog box doesn't load properly, it overlaps each other command buttons and the worst part is it hangs. does it have to do with the browser cuz i use ie9 and the program was design for ie8? or is it the OS i used because i am using windows XP? ALSO does ie8 not compatible with VISTA?