I have the 2.8 GHz, Mac Pro Xeon 8-Core. It came with 2GB of ram, and I added after market ram (Kingston PC2-6400 800Mhz DDR2 ECC buffered 2GB x 4), I have two slots left that I'd like to fill up with the same aftermarket ram. Unfortunately, this ram is apparently harder to come by now then the last time I picked them up at my local computer store. I'm wondering, does it have to be DDR2 or can I use DDR3 ram on my machine? And does it have to be ECC? Does ECC or non-ECC make a difference if I'm not using my system as a server? They ram I have in there now is ECC, can I mix in non-ECC with it? Thanks.