First of all, your system has a nonstandard power supply, the same size and with the same connectors as an ATX power supply, so if you changed boards you'd have to change the power supply. Then, because you have a custom front panel connector, you'd have to rewire that for a different board. On top of that, the port opening in your case is too small for most newer boards, and a standard backplate won't fit. Old boards will, however.
Your only option is to either build a completely new system, or upgrade that one. You try to find a 1.4GHz upgrade kit at Powerleap, OR you can add a 1.0GHz Coppermine core PIII. Coppermine core PIII 1.0GHz have 1.65v, 1.70v, or 1.75v cores, Tualatins require an adapter and have 1.475v cores (or thereabouts).
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