Operating System: Windows NT 4.0 (Note: might work with other versions of this os.)
1. Double click on 5400PC4E.exe
2. Follow the on-screen prompts to extract the driver files
3. Launch Add Printer Wizard
4. When prompted for the Manufacturer and Model click on Have Disk
5. Browse to the following location "C:\OKIDATA\5400\NT4\PCL\English"
6. Click on OK
7. Follow the prompts to finish the driver installation