O.K. I thought maybe it was possible that your mobo supported PXE booting.
Sometimes, depending upon the BIOS, you have to turn something on in another field before you can select PXE or network booting as an option in boot sequence.
Sometimes there is a legacy network boot and when PXE is turned on you can use another style of network boot (Nvidia boot rom, PXE boot, some other name).
However, since your mobo is vintage 2002 (approx.) I doubt whether it can PXE boot.
I could not find a manual (at least from a trusted source) to double check, but, you probably have.
From what I have read the manual is about 120 pages.
Thought I might save you some work from having to build a PXE or gPXE disk.