yes, this should work. Both of those machines are of the same generation, both have the processor on a separate daughter card. And since the upgrades that have been available in the past for that generation of iMac don't distinguish between daughter cards for the 233-333 mhz machines, it would appear to just be a straight swap.
Don't forget to take the ram from the 233 mhz card if its got more ram from than the 333 or if the 333 has one of its slots open.