Appraently Sharepoint 2003 ruins zip-files. A pain that gave my sp2003 installation an extra challenge. As if Sharepoint hasn’t given us enough of those:
“A common question that I see in the Microsoft Public newsgroup on Sharepoint Portal Server is when companies decide to put zip files in Document libraries and then once downloaded become corrupt. The route cause of this problem is actually IIS and not Sharepoint hence this Whitepaper will show you how to change the settings in IIS in order to support Zip files without corruption.”
Read the attached PDF to view the sharepoint zip-solution.