yes, this is known as a dualboot. You can put them both on the SSD if you wanted.
EDIT: im not sure how it would work actually with 2 drives. You might have to put them on the same drive. can someone answer that? would you be allowed to select which OS if they are on separate drives?
(sorry OP, but imma leech off your thread a bit to learn this myself )
If you installed 7 to the hdd, and you still have the same motherboard, you could back up your data and use the disc to fresh install 7 to the new ssd.