Here is a tutorial on how to compress and uncompress files.

http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3169372&ebot_calc_page#message_3169372

The tutorial explains how to compress them, but the method is the same for uncompressing. Just pick "uncompress files" instead of "compress". 

You can use the browse window to locate the Materials folder, or even the sub folder inside it that has your actual files in it, if you don't want to uncompress the whole runtime.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi