Computer crashes with additional RAM

Hey all, I have an ASUS P4P800 motherboard with 2 clips of PC3200 512 mb ddr ram (same exact type, manufacture, etc). When both clips are installed, I get random system crashes. When I take 1 clip out, my system runs fine. I tested each clip seperately without errors, so I know there is not a problem with the ram itself. The same EXACT thing happened with my old ASUS A7V266E with my PC2100 RAM. My system would work fine with 1 clip, but would crash with both clips. Any ideas? I'm thinking that I need to change my latency or voltage settings with both clips installed. Does this sound like the problem? If so, are there any recommended settings I should try? Is it reasonably safe to play around with these settings without damaging my ram? Other relavent information: P4 2.8 Ghz, Windows XP Professional, 430 Wt Antec PS. Thanks in advance.