Your computer is most likely using the original DDR and it isn't impossible it is using Rambus. I am fuzzy on this because it has been a while but I think it is like PC2700 DDR for those old P4 boards.
Well there were different P4 with different sockets. If you can open your computer and see the label on the memories then you'll know it. Other option is to use CPU-Z as it reveals all hardware information, CPU, DDR, Graphics.