If you plan to move to a new, high end motherboard, you'll need a new CPU and RAM to go with it (and more than likely a new power supply as well). The chipsets and sockets (where the CPU plugs in) on motherboards have changed many times since the Celeron 766, so any up-to-date upgrade you plan will result in many components being replaced.
If you just want a new motherboard for your 766 Celeron, then there isn't much point, because it won't give you more than a couple of extra frames per second in games. The motherboard just provides a means to connect everything in a PC together, allow communication between them, and maybe throw in the odd extra feature here and there (overclocking, onboard sound/video/network, etc). Of course, newer motherboards are considerably faster, but you need the newer and faster compatible components to make use of the speed!