Ok, I'm typing this on my Optiplex 745 running the q6600. I tried upgrading RAM, as others have stated they have working 8GB @ 800MHz in their 745's, but I'm getting nothing. I got 4x2GB Samsung DDR2, but I get no Post with even just 1 of them in. I suppose I may have purchased one of those "AMD only" memory packages, but for the life of me I never remember seeing this Intel or AMD Only in memory until a few years ago... Anyways... I was hoping someone who has gotten modules 2GB PC2-6400 to work in their Q6600 Dell 745, please can you post what type of memory you purchased?