Good news: You will be able to get the PC using the Mac's USB printer if you're willing to either leave them both on, or turn them both on before use.

Or you can buy one of those little ethernet-to-usb printer sharing boxes so the mac doesn't have to be left on. I've had mediocre experience with them (tricky to configure and keep them working but you're going to be paying someone to do that for you).

The tricky and time-consuming part is going to be downgrading that PC to windows XP (specifically getting all the hardware drivers working properly). You might be paying someone the 100.00 for that alone, and another day's session for all the other stuff.