LAP TOP UPGRADE QUESTION

Which sony??
You would benifit more by maxing out the memory. As to the CL rating, that depends on the BIOS ie is the BIOS locked, or will it use the info stored on the memory sticks (SPD) and adjust the timing. If you upgrade to 2 sticks of 1 gig it will not hurt to go for the better CL rating (Lower is better).

Added: as to speed. You can increase speed as long as the SPD indicates that it will run at your Bus speed (267 MHz). Most DDR2 667 (Bus freq = 333MHz) will run at the lower freq, but at a lower CL rating. This way if your bios does not change the mem ratio, the memory will still work. As I indicated the increase from 1 to 2 gigs ram will be a better performance boost than going for 1 gig at a higher freq rating.