I want to boost the amount of memory I have in my PC. The machine is a Compaq Presario SR1420UK with a K8S-LA (Salmon) motherboard in it. I currently have 512MB, and want to upgrade to 1GB. What I don't know is if I can just purchase any PC 3200 DDR and add it, or are only certain brands compatible? Also, is it possible to buy just another 512MB and add it to my system, or will I need to buy 1GB and replace the current memory?