Confused With Max RAM Capacity

I been trying to upgrade my machine's RAM from the 386MB that it has installed to something like 1.5GB to more (like 3GB) but the thing is that I been searching around all over the net and the biggest RAM stick I can find for my model is like 0.5GB. I only have 3 slots with 2 of them filled making up for the 386MB. I went to Crucial.com and tried checking with them to see which type of RAM would be best for me, but my "exact" pc model isn't listed there, so I rounded down a serial number (similiar to my # model) and it recomended 1.5GB. The thing is that I also used their Crucial Scanner to determine what type of RAM and the results said MAX CAPACITY 3072MB. The question I have now is, can I, or would I be able to max out the RAM capacity to 3072MB or would I be limited to a 1.5GB?
If it helps, the 2 sticks I currently have installed are 1.) SDRAM PC133 128MB and the other is 2.) SDRAM PC133 256MB.