Do not buy PC2-6400 (800MHz). The motherboard will downclock it to 667MHz, which is fine, but many high-density 4GB sticks will cause boot failures. Stick with 2x 1GB DDR2-667 for maximum stability.
One distinct feature of the VAIO VGN-CS series is its located above the keyboard. These allow you to control volume and playback (Play/Pause, Stop, Previous/Next) with a simple touch or slide of your finger, accompanied by glowing LED indicators. Sony Vaio PCG-3C2L Repair Help - iFixit sony vaio pcg-3c2l specs
Sony Vaio laptops of this era were praised for their industrial design: Do not buy PC2-6400 (800MHz)
Users frequently reported flickering or vertical color lines appearing on the LCD screen over time. which is fine