A USB key that boots like a Windows 98 boot disk is useful for BIOS flashing, firmware flashing, and other scenarios where WinPE or other environments are not suitable. Most machines don't have floppy drives now, and USB keys are much, much faster.
HP has released a utility for this purpose, and this can be downloaded here.
Alternative download links:
Additionally, you will need Windows 98 boot disk files, which I have included here.