usually most PCs have two slots for memories. So it is almost not possilbe for you to insert more than two memories if you only got two slots.
Also it depends on your CPU, For example: "memory for CPU 1.8" can be installed on "CPU 2.8" and stil works, but if you install "memory for CPU 2.8" on "CPU 1.8", it will not work at all. Which you can find when you right click "my computer" - properties.
so your Pc 100 or pc 133, the number is the Mhz, which equals to CPU 1 or CPU 1.3.
