Hardware trouble, someone help?

I have had my computer for almost 6 years. One day my father had the great idea to send to garbage all of the instruction booklets and diskets I had for information of the computer's interior (ram memory, graphic card, CPU and all this stuff). Nowadays that I have decided to make this slowpoke snail run a bit faster, I have no clue what graphic card and ram memory its motherboard is compatible with. Anyone know how I can see this compatibility? I mean, is there any programme allowing me to check the requirements? All I know is that my RAM is a DDR of 256 Mb and a CPU of 3Gh and again 3Gh (don't know why this is double). Anyone help me?