The amount of RAM that you can plug into your machine is not determined by the processor but by the motherboard and/or chipset. What are your specs, mobo, chipset?
With your mobo having 3 DIMM slots, you can put 2GB of RAM just by using 2 DIMM slots and 2 x 1GB sticks of memory, leaving the 3rd DIMM empty.
You can get a 1GB PC2700 memory from www.newegg.com for anywhere from $30 to $45, or a memory kit of 2x1GB sticks for anywhere from $65 to $85. If your mobo chipset supports dual channel memory, you're better off buying a kit.