Fwah socket PGA478.. Same as my first PC.
Ok anyway, your motherboard can only supports maximum 1GB stick on each slot for a total of 2GB. 1GB DDR RAM stick is quite expensive TBH. What stuff are you doing with this PC btw?
I don't really see a need to upgrade RAM as i've experimented it on my old PC on same era and the Pentium 4-grade CPU will bottleneck the overall system performance before RAM capacity does. That is to say, the amount of different programmes you opened will get (severely) choked by the poorly performing Pentium 4 processor way before your 2GB RAM gets fully occupied. On my old PC, the CPU constantly runs at 100% load on Windows XP just with internet browser while my (total of) 1GB RAM barely uses over half of it.