Networking :: BIOS (>2.88MB) Flash Over PXE

I have a problem with flashing a BIOS. I have to use PXE to boot the computer, which actually works fine through syslinux. I also managed to find a FreeDOS floppy image (1.44 MB) that will be booted using syslinux.

The problem is moving the BIOS rom on to the computer to flash. For roms that fit on to the FreeDOS img it works fine if I just add the rom and the exe for flashing to the floppy image. But one of the roms I shall work with is to big to fit even on a 2.88 MB floppy.

I found a "Howto: BIOS-Update per bootable CD (Method II)" for creating a bootable iso holding the DOS image and the additional files for flashing. Using a syslinux configuration like Code: default boot prompt 0 label boot linux memdisk initrd 20101201_091658.iso append iso the iso will be transfered to the client and I get an "A:>" DOS prompt.

According to the HowTo I should be able to switch to drive of the "cd" and access the rom file there. I've tried all drive letters, but all I get is "Invalid drive <letter>:.". I tried booting the DOS with more drivers (FDCD0001 as CD-ROM driver) but it says "No CD-ROM drive to use; XCDROM not loaded!". Additionally it promts: "SHCDX33A installed. o drives assigned. 2 drive(s) available." Here is the question:

How am I able to reach the files from the iso that are not included to the DOS image?
Or maybe there is another way to flash a large BIOS rom over PXE?