Excel Auto Formating

If this has been asked before I'm sorry but this has been driving me nuts for awhile now.

I run an online store where all the product details are handled by a .CSV file and naturally all the information has to be exact or it won't work at all especially UPC codes and product codes. However whenever I open the .CSV file to edit anything it auto formats several bit of information including several UPCs and product codes that begin with one or more 0's. This among many other problem I have had are all caused by excel's auto formating "tool" and I find it of absolutely no use. Is there any way at all to disable this "tool" so it will stop messing with my data every time I need to make a product change? (I have tried using the '0 trick but when I save the file and open it again later all the '0s are gone again)

I am running Excel 2007 on Windows Vista SP1