Adapting 'Simple Custom Scrollbar'

i would like to use this tut:
http://www.kirupa.com/developer/flash8/scrollbar.htm

what i really need to do is adapt the code to load an external .txt file and use the dynamic content to create the contentHeight.

problem is, can i load into the mc to create a height dependent on the .txt file i load?
the dynamic txt box height is fixed!

i hope that is clear
rat