Question about Hard drives with different OS on them

Hey reddit,

I built my first computer a few weeks ago, and due to being on a budget, I decided to re use my old hard drives (one from my old comp, and one from another comp) and my old cd drive. The computer works great, but the problem is that one of my hard drives (the other is fine) and my cd drive use PATA cords, while my motherboard is SATA only.

So I bought 2 adapters today, I should probably be able to get the cd drive right, but my question is about the hard drive. My current working drive is running windows 7, while the hard drive I wish to use is has XP on it...my only use for this hard drive would be storage pretty much.

How will this work after I hook it up? Can I delete the OS from it after installation and use it just as storage for my games? Thanks in advance. <3