You could have a look at www.lowendmac.com and www.xlr8yourmac.com for ideas. I did see some discussion on clocking the eMac CPU once.
I believe you have a Radeon 9600 with 64 MB video RAM, so your graphics are just about up to the task, and your RAM sounds OK. But unless you can get well over 1 GHz CPU performance I imagine you'll have problems running Civ4. However, all this is speculation, based on hints from Brad and the experiences of PC players. We'll have to wait until Aspyr has done some optimisation and testing before we know what the min specs are.
I believe you have a Radeon 9600 with 64 MB video RAM, so your graphics are just about up to the task, and your RAM sounds OK. But unless you can get well over 1 GHz CPU performance I imagine you'll have problems running Civ4. However, all this is speculation, based on hints from Brad and the experiences of PC players. We'll have to wait until Aspyr has done some optimisation and testing before we know what the min specs are.