The best way to do it is to make a new partition on your second partition. approx 32GB should be enough.
If you then run the Windows 7 dvd from your c drive it will install Windows 7 direct from Windows. Make sure you choose customise installation NOT UPGRADE. Just point at the new partition NOT your c drive.
You can also boot from DVD and install in the usual way. Doing it via windows works just as well and it does not get the dual boot table wrong.
I named the new partition Windows 7 on mine that way you cannot get it wrong. It should take approx 30 minutes to do the installation.
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