Need to modify a netinstall iso to add one directory

[Benton Lam <calyth2004@shaw.ca>]

I've tried to recreate the iso image using mkisofs after adding the 
directory, and used the instruction for isolinux. The CD can boot, but 
then the installer complains that the cd is a non-debian cdrom.
I need to do this because I'm helping out a linux demo at school where 
we want to give them a cd that has a debian netinstall and cygwin, in 
case they still have cold feet from trying to install Linux.
Please suggest a solution as soon as you can. I'll need to create this 
image as soon as I can and burn about 50 of them by Friday.

Thanks in advance!

Benton Lam