Well I've tried every suggestion on this topic and still I can't get this particular MD to pxeboot properly. I've tried to develop an understanding of the process of network booting PXE clients, and read some good wiki documentation on the subject, but there doesn't seem to be an indepth documentation of the process from start to finish of the process.
I tried playing around with manually creating the directory and file structure needed to boot, i.e. I created a file called 01-{mac address} in the pxelinux.cfg directory (actually copied from another MD and renamed to correspond to failing MD's mac address and modified it with it's device #), manually created a directory called /tftpboot/{device#} and copied vmlinuz & initrd.img into it, plus created a directory called /usr/pluto/diskless/{device number}. This seemed to work up to a point. The MD would boot, receive it's assigned IP address, load vmlinuz & initrd.img, but then would stop with an error saying it could not mount pre-exportnfs (can't remember exactly now).
I also tried creating the MD manually in lmce admin, put in the mac address and "setup diskless w/s" but this didn't work either.
So if any of you gurus out there who might have any experience with the pxeboot process can point me in the right direction I would appreciate it very much.
BTW, I think I will try to put in a pci 100mbit ethernet card into this MD once I can locate one and see if it can boot with it. I wonder if the whole diskless MD creation thing is fubared or if it is just this one MD.
Fins