Then you should only have 1 hard drive plugged in at a time, and control which one you want to boot from, from the bios.
Do you have another key to activate windows ?
You should be using the 2nd drive for storage, not for another install of W7.
Use a fresh ISO for your licensed version and the tool to write to flash stick in Steps 1 and 2 of Clean Reinstall - Factory OEM Windows 7. Look over the other steps which will help you get and keep a perfect install.
Why do you want two Win7 installs? If you insist then I'd unplug the existing OS's HD, boot the installer, delete D partition during install, create a new 100gb OS partition and then partiiton the rest for storage. To do this partitioning during install use the Drive Options pictured in Steps 7 and 8 of Clean Install Windows 7
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