, this will list a load of info on your pc and give us details of your motherboard under the 'mainboard' tab; think the american megatrends relates to a chip on your mobo?
Have you tried reseating your graphics card?
Does it have a fan on it, as some of those cards are 'silent' so just rely on a heat-sink to keep them cool; could point a spare fan at it and see if that helps?
If you have a E4500 CPU then your current motherboard won't support the X4 955.
In terms of RAM, you'd probably only see a couple of FPS increase, if that, moving to 4GB at the resolution you're talking about gaming at; unless of course you plan on overclocking your CPU, then your RAM speed will come into play.
In short, the spec of your PC is going to be influenced by what resolution you want to game at, which is going to be set by your monitor.
If you're gonna join us on BFBC2 and BF3 (when it gets released) then a quad core would give you more grunt, as these games can utilise 4 cores.