disk utility - unable to scan dmg

okay so i'm trying to restore an image of a windows xp disk onto a usb stick to install on my netbook

made the dmg from the cd and to restore it to the usb drive you need to scan image for restore

but, it won't actually let me do that, it says

unable to scan blahblah.dmg invalid argument

i am about to send the computer out of the window...help?

i've just done this with the snow leopard disc and it worked fine

not sure why it has a problem with a windows cd, SO ANNOYING