umm easiest way to tell what ram you have is to pull it out and count the pins and notice where the grooves are. this will determine DDR, DDR2, RDRam, SD Ram, Simms etc. as for speed it is hard to tell that without knowing codes on the stick, what motherboard do you have? this can also determine what memory yuou are most likely running or should be running. with a Athlon 64 you are most liely running DDR or DDR2 speed can be anywhere from PC1600-PC6200 DDR or PC2 3200- PC2 8500 on ddr2
my AMD is running PC2700 DDR but my P4 is running PC2 4200 DDR2