If you just want a backup, then split up the folders on the DVD so that they will fit on CDs. If you want to be able to install by using multiple CDs, then I think you would be better off trying to find windows 7 already on CDs.
However, now that I think about it, if you remember where you put the files, you might be able to split them onto different CDs like I said above, then pop in the CD with the boot sector and base installer on it, then when it can't find the file it wants to copy (assuming it doesn't crash) you can pop in the next cd and go.
I remember doing something like that with my copy of windows xp, though it did come on two CDs so the installer was probably designed to work that way.
Though that too would be a lot of work, and I have no idea if its even possible. Just a thought.
-Bucky24