Create a data partition on your secondary HD, copy the User folders into it after sorting all of your data into them correctly.
After confirming all of your data is there in the secondary HD Data partition, unplug it during Clean Install Windows 7
to the target HD: Boot the installer, use Custom Install drive options to delete all partitions on the if you don't need them as shown in illustrated steps in the blue link.
Then after Windows 7 install plug back in the data HD. If you want to keep your data on the secondary HD and link it to Windows 7 rightclick on each User folder to add it to the related Library - Include a Folder - Windows 7 Forums.
If you want to copy the data into the Windows 7 OS User folders then open each from the data drive, from Organize tab Select All, then drag the file group to the corresponding Windows 7 User folder under your User name in the C drive. Make sure you hold the left click until the left-hand Explorer bar finishes unfolding and confirms you're copying to the exact folder wanted.