Your motherboard uses DDR ram either pc2700 333MHz or pc3200 400MHz. It should be on a sticker on one of your memory modules.
Module didnt show the pc numbers but I got the model info which allowed me to search it. Yep, it's a kvr400x64c3a pc3200/256 ddr400. So should I be able to simply replace one of the modules with the 1gb upgrade card, or am I missing something? I'm obviously not very tech-literate, but I'm trying save some money by doing this myself. I appreciate your help.