Just about all powersupplies now days have 24 pins. If in question, look for "ATX 2.0". That's the actual name for the ATX with 24 pins.
As for Windows, sure. I install XP on those chips all day long. Yes you can get a 64 bit version of XP, but it's basically not worth it for such a low end machine and it requires 64bit drivers for all your hardware.
Steven