Dell Precision T5400 (Late 2007) - Manual (Page 100)

100 System Setup
Floppy Drive
1 In system setup, set the Diskette Drive option to USB.
2 Save your changes and exit system setup.
3 Connect the USB floppy drive, insert bootable media, and re-boot the
system.
4 See "Selecting the Boot Device for the Current Boot" on page 98.