After installing Service Pack 4 my ATAPI/IDE ZIP drive is not available.

A. This seems to be caused by the drive not being assigned a drive letter. To resolve perform the following:

1. Insert a ZIP disk into the drive
2. Start Disk Administrator (Start - Programs - Administrative Tools - Disk Administrator)
3. Right click on the ZIP drive and select "Assign drive letter"
4. Select a Drive letter (e.g. H) and click OK
5. The change will take effect and the drive should now be visible from Explorer.