Upgrading DDR RAM

I almost bought a 1G DDR333 PC2700 SODIMM RAM on eBay before I tore the machine apart and realized that the maximum memory for my laptop was just 768MB and may only be compatible with PC2100/DDR266 chips running at 133 MHz (peak data transferring rate at 2.133 GByte/s). Those 512MB PC2100 DDR RAM sticks on eBay are now around CAD$70, shipping cost included.

Sony VAIO PCG-Z Series PCG-Z1XZC Memory
System Memory Configuration

Standard Memory: 256MB (Non-removable)
Maximum Memory: 768MB
Expansion: 1 Socket
CPU & ChipSet: Intel Pentium M 1.5 GHz Intel 855PM
Bus Architecture: PC Card
Mfgr's System P/N's: N/A