This system will take up to 2GB's of PC2700 DDR Memory and has 4 sockets in which to do so. It's suggested that you install them in pairs but is not mandatory.
APPLE Part# M8832G/A Compatible 256MB PC2700 DDR DIMM
$25.00
APPLE Part# M8833G/A Compatible 512MB PC2700 DDR DIMM
$50.00