7970 will work just fine if your doing going to use it to connect to a monitor or TV.
For password cracking not so much. It has the power but your wont get the same possible number crunching that the machine can do as a physical box. Unless your running x2 physical CPU's in the box. That tiny bit of cpu time required will be noticed if your doing this on a home machine for academic purposes. Theres other much more prefered methods of doing it but if you dont care how long it will take or the added delay isnt an issue then by all means have at it.
Now be quite you 
you let some other peoples purposes be known to the world...