When I got a Mac Mini, I used the keyboard, mouse and monitor from my PC.
BUT -
you have to plug the keyboard and mouse into a USB port, so if they have the old kind of connection (I think it was PS/2), you'll need a converter. I think Radio Shack sells them.
AND
The shortcuts aren't the same if you use the PC keyboard. For example, on a PC you press the CTRL key and the P key to print. With a Mac, the CTRL key doesn't work; you need to press the key next to it. My fingers can find the CTRL key, but can't find the key next to it unless I look.