Ok, first off, the imac controllers are different. If you check the mac site, the later imac G3s can hold up to a gig, yet they only have two slots. So they will run 512s...
Anyway, the maximum RAM a G3 b/w can handle is 1gig. And CanadaRAM is right (as he always is with RAM questions), I am yet to find a 512 stick that works in my b/w. Good luck if you decide to, but honestly I'd advise taking the advice in this thread and only buy those sticks if you have another machine you can use them in or you can resell them/return them.
And btw, I'm personally yet to find a 1gig PC100/133 stick that works in a G4 tower, much less a G3.