Well you can download 7 from "digital river." But you have to PAY for it.
Then use a DVD program to create an ISO disk.
I use NERO to make ISO disk. It actually worked pretty good.
But it may be easier to get a real DVD from Microsoft...
"microsoft software for students" will sell you 7 pro for about $40. And, this includes the backup disk.
But you MUST have a student e mail from your college, etc...