Laptop Dual Boot??

Hi there,
So I have a relatively new laptop (got in in April)
It has windows 8.1 on it currently.

It also had a spare expansion slot for an additional hard-drive.
I have tossed into this extra slot a HD from an older laptop which had windows 7 on it.

Is it possible to set up the laptop to dual boot? If so how?
Will the laptop work with windows 7 (I realize I'd have to find drivers for pretty much everything so is this task feesable?)
Or ultimately would i be better using the spare slot for an SSD and putting the OS onto that??

Thanks for your opinions/help :)