Don't do that. Your FSB is 200MHz, not 266MHz, so leave it as it is. However, your Core voltage is a bit high at could be the reason for your semi high temps. It should be 1.75 volts. This can be due to a wrong setting in your BIOS. so check that the core voltage is set to 1.75V. If that is set correctly, then if your BIOS supports hardware monitoring, have a look at check how the other voltage rails compare to what there ment to be. ie, 5v rail no higher or lower by 10% etc etc etc. If it is, perhaps a PSU replacement is in need. If all the other voltages are within the 10% tolerance, perhaps it's the motherboard thats the problem. Unless it is causing stability problems, I'd not bother going to the expense to replace it.
Also, as someone else has already mentioned, if you've never gave your system a gentle clean out - remove dust a grime build ups from fans, heatsinks and airflow ways.
As for the Motherboard giving wrong readings for your CPU, it's probably just one of those BIOS software bugs getting confused over a non-PR rated CPU and a PR rated CPU. But, if it really thinks its an athlon XP, it could indeed be deleberatly putting up the voltage. If you can, force it down to 1.75V.
Hope this helps