RAM For My Friend's Laptop

This question concerns buying DDR RAM for my friend’s 3.5 year-old Sony p4 laptop which currently has 512 MB of PC2100 DDR RAM (2 sticks of 256 MB) The 512 MB is shared with her graphics and the laptop runs XP slow.

I bought 2 sticks of PNY 1 GB PC2700 on sale and tried it in her laptop. It speeded the laptop up considerably, but only utilized 512 MB of each stick. Apparently, her laptop’s memory is upgradable to 1 GB max. So I returned the memory and will order two 512 MB sticks instead.

Newegg has PNY PC2700 512 MB notebook memory for $27 and has Kingston PC3200 Kingston 512 MB notebook memory for $31.

I know that in my p4 desktop, I can use PC2100, PC2700, and PC3200 but I’m not sure if laptops are different. Will PC3200 work in her laptop (which came with PC2100 RAM)? If so, is the difference in speed worth the extra $8 (for 2 sticks) to get the faster Kingston RAM?

Check your manual see if it supports DDR400(PC3200) …
if no manual check their website or Dl’d CPU-Z tool to get info on the system…