|"it doesn't "hurt" the computer or the "memory chip" by trying to install the wrong one does it?"|
What do you mean by "wrong"? SDR-SDRAM has 168-pins, DDR-SDRAM has 184-pins, DDR2-SDRAM has 240-pins. Obviously you need to use the "right" RAM.
You need to get the motherboard specs & find out which type & amount of RAM is supported. If he currently has only 128MB, that's pretty pathetic. I assume it's an old Win98 machine? XP NEVER should have been installed on that machine in the 1st place.