Does the computer have COA (Certificate of Authenticity) sticker on it?
The sticker will probably be yellow and have the word Microsoft on it.
The other question is whether the computer's components function, especially the hard disk and the ram and how much ram the computer has.
As suggested, a simple, free version of Linux will help you here. PuppyLinux comes to mind.
No matter which version of linux you use, don't worry about understanding everything, Just stumble around enough to find out what you have bought.
Puppy Linux is nice in that it can be run from CD without installing anything on your computer.