Thanks for all your help, IatricSB!
Two things:
Actually it's quite easy. What is in your zip file, will be in your web space after unzipping. When there is a file in your zipfile and a path name is stored with the file, the file will be in the corresponding path in your webspace. That's all. And that's the most flexible and complete solution.
Second issue: You're right, if the server tries to unzip the file just in the moment when you're uploading it, it will not be unzipped (of course, because it's not complete) but it will be deleted nevertheless.
I'll try to change that.