YOu can reinstall retail Windows 7 wherever and as often as you want.
What I'd do is follow these same best practices for Clean Reinstall - Factory OEM Windows 7
to the SSD.
Depending upon the size of the SSD you'll want at least the programs on it, but if space is or becomes limited you can move to or leave your User folders on the HDD and simply link them from Windows 7 to their related Library - Include a Folder - Windows 7 Forums.
When ready to delete the OS on HDD, you can do this while keeping the data on it by shrinking the OS partition, moving the data to a new data partition you create then, then when ready delete in Disk Mgmt the old Windows 7 partition on HD to create a new partition, or resize the data partition into the deleted space: Partition Wizard Resize Partition Video Help.