Some people have discovered that when they try to attach zip files to email, Outlook 2003 can't 'see' the files. They see every other file in the File Browser dialog except zips.

This is related to the Compressed Folders utility included in Windows and it's ability to view zips as folders. You'll need to unregister the zip handler or drag the zips from Windows Explorer to the new mail window to attach them.

To disable the feature at the Start menu, Run command, type:

regsvr32 /u zipfldr.dll

To restore the functionality, return to Start Menu, Run command and
type:

regsvr32 zipfldr.dll

See http://www.slipstick.com/problems/zip.htm  for more information