For anyone who needs it, here's Dell's technical guide:

http://www.sayresd.org/wp-content/uploads/2015/12/PC-Dell-De...

There are some Amazon sellers who have put together complete systems running Windows 7 or 10 for around US $100:

https://smile.amazon.com/Dell-OptiPlex-FX160-1-6GHz-Windows/...

If you're buying one to use as a server this won't matter to you, but if you want a tiny Linux or BSD desktop, you may want to look elsewhere. The video hardware is SiS Mirage, which has terrible support in non-Windows OSes.