No offence, but unless you're going to invest time learning about circuits and troubleshooting circuits,
and hundreds of dollars in equipment and test gear, you're going to find it hard to assemble such a power
supply no matter how much help people give you over the internet.
As Godfrey mentioned, it is not possible to "adapt" an existing 220V PSU to your needs. Also, you're
presuming you need to now generate 320V, which is an incorrect presumption which no-one actually suggested
you do.
You could seek existing DC-DC converter modules that will supply DC 12V and DC 5V from an unregulated 12V source,
but they are going to be expensive - it may cost a few hundred dollars, depending on how much current
you need on the 12V and 5V rails.
You could try seeking some lower-cost DC-DC converters from ebay and experiment, but at least use a multimeter
and a dummy resistor to check all is well before connecting up your motherboard.
Why does someone need an atom server (!) to operate from 12V? If it is not from a battery, then just go the
easy route and buy a 12V->220V inverter. It is cheap and will work.