OK a couple of things: The PowerMac G5 tower needs RAM installed in pairs, whereas the iMac G5 takes singles. The 1.6 GHz is the only G5 Powermac that is specced for PC2700 RAM, but it will use Mac-compatible PC3200 happily.
Not all RAM that is compatible with the PowerMac G5 is compatible in the iMac -- the iMac is considerably fussier about the internal electronic organization of the module, even though outwardly the spec is the same.
As far as I know though, any RAM that works in the iMac G5 will work in pairs in the G5 tower or singly in the Mini.
Thanks
Trevor
CanadaRAM.com