Help With XML Preloader

I am trying to create some sort of gallery where when the next button is pressed it PRELOADS the next image in the XML in to the designated MC. I have attached a copy of the file so that what I am saying makes more sense. I have got it all working except for the animating of the preloader. Would someone mind having a look at the file and telling me where I have made a mistake(pretty sure it is with this part " preloader.preload_bar._xscale = 100*loaded/filesize; " But I can seem to work it out. Also if there is a better way of doing this I am open to sugestions.

http://www.arctosdesign.com/trial.zip