[syslinux] Pxelinux/memdisk with XP "MS-DOS" boot disk

[dpetersen55 at new.rr.com]

I'm trying to use this universal DOS TCP/IP boot disk available here:

http://members.iinet.net.au/~bdriver/bootdisk/

It requires an MS-DOS formatted disk created by Windows XP.  It works great as a floppy but doesn't boot at all with memdisk.  The problem can be simplified down to just the XP boot disk.  If you make an MS-DOS startup disk with XP on a floppy, dd the floppy to an image file and try to boot it with pxelinux/memdisk, it hangs.  It just says "Starting..." and won't even respond to ctrl+alt+del.  I've booted lots of PC-DOS, MS-DOS, Linux, and BIOS flash disks with no problems, but this one just won't run. 

Any ideas how to debug this?