Moving files to the second drive is a good idea. Because the second drive is subject to less activity than the C drive, moving the files reduces the chances that they will be clobbered in the case of a major system failure. While there is no need to add any software to your second drive or your Zip drive in order to use files stored on either of them, you should do a complete ScanDisk of the second hard drive to check for errors and physical problems. I would even reformat it. Don't be concerned if the next time you try to access a moved file by opening it from the list in Word's File Menu you get a message that the file is missing.
Word only remembers the last location where the file was stored.
The next time you open the file, Word will have a record of its new address.