Outlook Express/MSN Breaks up Attachment

I have a friend who uses Outlook Express (4.5) with MSN. Everytime he tries to send me an attachment (Access or Zip file), it imbeds the file into the text of the message and adds a .txt attachment. It also forces him to break the message up into many parts. I cannot find the proper setting(s) to change to fix this problem. Any assistance would be greatly appreciated!