Actually, I think the tables are wrong in this case. The board's TPS says X3000 series Xeon processors, as well as Core 2 Duo and Core 2 Quad processors, are supported, but the tables don't list any of these as supported (and should). Regardless, this hardware is so old that, even with overclocking, a modern Atom processor is likely going to kick its a$$. As far as this endeavor is concerned, I don't do or believe in overclocking so I cannot provide any insights into how to use the BIOS parameters for this and I do not believe that XTU supports processors this old.
How much you can overclock is going to vary from one processor to another. Regardless, this system is 9+ years old and on its last legs. If it is really going to to be used by children, why are you jeopardizing its continued existence trying to overclock it?