exact permission settings

what are the exact permission settings for IIS and NTFS to get your script working properly: I guess for IIS, it's read, write and script only execute, for NTFS it should be RWXD. for the IUSR_machine where the webserver is running. Is this correct?

Yes, if you want to have full control over a folder with WebExplorer Free, the folder should have NTFS read, write, delete (full control) permissions, that way all file operations can be done. If you want to enable downloading, the folder should have IIS read permission and should have IIS execute permission for enabling script execution with a click.
For the webexplorer folder(the folder where webexplorer.asp resides), IIS read and script only execute permissions are enough and no specific NTFS permissions are required.