i have a WinME .iso sitting here on my desktop. i mounted it so it's a disc and i can see what's in it. i tried to edit it, but i have to be logged in as root to do it. stupid OSX.
so it can probably be done. i would say log in as root, edit the image, save it as an .iso, and reburn it.
not sure it will still boot, but i don't see why not.
just be sure to only edit the files that you don't need. in your case, if the win2k is designed only for a Dell computer, that might be a pain in the ass. there's a very good chance it's going to only install on a Dell, as key files will be set up Dell only.
it might be a lot easier to just *cough* find win2k *cough* on the 'net.