Youll only be able to do software RAID (through windows not controller) as "hardware" will require drivers to be installed in windows, and will most likely BSOD on boot anyway.
With any hard drive changes you always run the risk of something going wrong and loosing data hence why you "should" always have a backup, not everyone does this obviously.
To be honest your best of putting the second drive in a external casing and using it as a backup. Or if you want a performance increase to set them up in RAID-0 (striping, will require reinstall). RAID-1 is rarely useful for home PC situations.