You do not have to install the system, the files are already there. What you have to do is make the C: partition active, so it is bootable, then run a startup repair from the Install DVD to fix the boot.
If you don't know how to do a startup repair, boot to the Win 7 Install DVD and select language, then on the next page, select repair from the lower left of the window.
Unless of course, I am misunderstanding your original question.
Any questions about procedures or command line options, post back. We are here to help.