Well, I was going to check out newegg.com and tell you what the fastest
chip you could use was, but they don't even sell 266 chips anymore.
You must shop at a different newegg than the rest of us.
They certainly do sell a few, over a half dozen, though I'm not
guaranteeing the board will run all the newer ones.
My advice, you can get a new motherboard for less than 100 bucks, far
less, do that.
then you can have 2 systems instead of a chip sitting on a shelf
A new board isn't a bad idea, but for feature and performance
benefits, not merely to run a faster CPU. Given the inclinaton
to adjust multipliers the OP could probably buy *any* CPU and
just run at the highest fsb the board supports, 266, and higher
multiplier to result in same CPU rated MHz speed. There are some
that aren't unlocked anymore though, so some Google research of
bridge unlocking would be prudent.