Imac Memory Ugrade Question

I have a 24" Imac with the 2.8 Ghz Intel Core 2 duo processor that I am a bit confused about upgrading the memory. I currently have 4 gb of memory, 2 per slot and would like to add more. According to OWC i can add a 4 gb chip to one slot for a total of 6, but the way I read the Crucial website the limit on this computer is 4. Any ideas as to which is correct, and how much memory exactly I can use in it? Thanks for any help.
Joe

 

Thank you very much for that link. I guess it explains the discrepancy between the two websites. I'm off to buy a 4gig memory module. Thanks again
Joe