Parallels Desktop for Mac supports external USB floppy drives in your guest OS. Just plug the USB drive to your Mac computer, connect it to the Virtual Machine using "Devices" menu on the menubar and it should be showed up in the guest OS as new USB device.
If your guest OS doesn't support USB floppy drive or you need to boot VM from floppy, you need to create an image file of your floppy disk at the MacOS X computer and connect it to the VM as virtual floppy drive:
- Open "Finder" -> "Applications" -> "Utilities" -> "Disk Utility".
- Insert source diskette from which the FDD image should be created into the External USB Floppy 3.5 disk drive and connect the device to the idle USB port of your computer.
- Select that floppy from the "Disk Utility" device list.
- Press "New Image" button on the top of the Disk Utility window. Select name and location for the image and set "Image Format" and “Encryption” to “read / write" and “none” respectively.
- Press "Save" button and wait for the image creation process to finish.
- Locate your created image, right-click on it (or Ctrl+click) and select "Get Info" option from the pop-up menu.
Expand "Name & Extension" section, change file's extension from ".dmg" to ".fdd", press ENTER, then press “Use .fdd” button in the pop-up window.
- Launch Parallels Desktop for Mac, click on the "Floppy" link in the Parallels Desktop window, check "Connect at startup" option and specify the floppy disk image file using "..." button. Hit "OK" to close Configuration Editor. Or you can connect floppy disk image file when VM is running from the "Devices" menu on the Mac menubar or using the icon in the status bar.