I have been battling these ZP 450 label printers for a very long time, and I finally figured out how to get them working.
As stated before, you need to download the most recent drivers from UPS. You need to register with them, but it is free.
This will lead you to a file download that puts the drivers and an installation file on your C: drive (C:/UPS Drivers).
Go into this folder and run the file PrnInst64.exe
You need to select the ZP450 at the bottom of the list, and also select the USB option.
The installation will run, but might come up with an error saying it wasn't installed correctly because their installation is faulty and does not actually assign the drivers to the USB device.
At this time, you can open the "Device and Printers" dialog from the start menu. You will notice that there is an "Unspecified USB Device". It is not in your printers, so you can't use it.
Right click on the unspecified device and select Properties.
Click the "Hardware" tab.
Double click on the item in device functions and navigate to the driver tab.
You then need to assign the driver to the USB device. These drivers are now located in the previously installed folder at C:/UPS Drivers/ZBRN/Win64. Navigate to that folder, and it will find the correct driver.
These instructions are from memory, and might not be exact, but this will give you the idea of twhat you need to do to make that unspecified device show up in the printers, and can now be used.
Shame on UPS and Zebra for not making a driver installation that actually works. Hope this helps you install these printers, and prevents you from throwing them at the wall. Good luck.