PCI bus

A fuse is a start. It would be more beneficial to just look over and look over your circuit and make sure there aren't any flaws or instances where you would be drawing too much current (Especially when you are working with an expensive motherboard lol. The PSU has pretty good support for shorts. I have done it a few times before unfortunatly, and all it does is shutoff your computer. It isn't great for the supply obviously.

The motherboard on the otherhand... I am not so sure. My guess is that it would not handle "things going wrong" too well.

try an LM7660 or 7661 as an inverter, you could also try googling Hamcomm as this interface does basically the same thing.

thx every body