Physically and electrically it will fit, whether it works is subject to whether the KVR (ValueRAM) build is compatible with the particular model iMac or not.
This RAM would NOT work in a 1.0 - 1.33 GHz AlBook for example, the chipset is not compatible with these Powerbooks.
Can't say whether this particular Kingston chip would give any trouble in the iMac.
Bigbertha: Is there some reason you are buying this generic RAM over a module that is guaranteed compatible with the iMac? (if it is used, or a very steep discount in price, it may be worth it to try. Will you have the right of return for refund if it is probematic?)