Old PC Laptop HDD with OS to Upgrade to Mac Mini A1176

I am upgrading my A1176 (late 2006) Mac Mini with new memory and a new superdrive (does not work) and Processor (T7200 2.0 GHz core 2 duo) and i found my old laptop PC hard drive that i kept when the motherboard went in it. it still has windows on it but was wondering if i could put that in my mini and still use the windows along with my OS X or do i have to erase it and just reload OS X fresh back on it so i don't have to buy a new bigger harddrive since i have this one. It is a 320 gig that is the exact replacement to my 80gig original. Thanks 🙂