network unattended boot from usb key

Having problems with this. I've used this useful HP utility to make a USB key bootable:

http://h18007.www1.hp.com/support/files/hp...load/20306.html

I developed an unattended install system for work which I boot via PXE using RIS. I use the system at home occasionally, and I have a laptop which I was trying to install using a USB key. The laptop is an HP which can only boot USB devices as if they're hard disks. Consequently it starts as the C: when booting from it, with the real HD as D:

The problem is that despite me setting the D: drive as the temp location in my WINNT.EXE command line, WINNT uses the memory stick (c:) as the Temp drive and copies all the windows files here first before trying to move them and expand the filenames on the D: drive. The other big problem is that you then can't remove the USB key after the first reboot because it has treated it as the System partition (Microsoft terminology). The bootsector, NTLDR and NTDETECT all end up there.

Is there any way to prevent this happening if the laptop won't mount the USB key as a floppy drive? I can't set the USB key to read only in the BIOS either. It's not a huge problem in that I can always use the floppy drive for the laptop but I had left it at work. And I'm not going to set up a domain with a RIS server at home...