util to use higher res than 1024x768


I saw a 3rd party util that would allow you to use a higher res than 1024x768 on an imac, but now I cannot find it. I have hooked it up to a larger external monitor, but I am still stuck at 1024x768. Has anyone seen this util or know where I can get it?
Originally posted by IAmNotMad
I think there was another that would work on OSX, this one does not does it?

Well if it is, it isn't widely availeble, tried all my sources, and couldn't find a thing.
But isn't it simply the iMac's hardware limit?
My G4 with 19" monitor goes upto millions in 1600 x 1200.