RAM slots do you have ? What type and speed RAM ?
Best place to get the right info is from your HP system docs or the HP system docs online.
Might suggest going to Win 7 first ... and then see how the PC runs on the new OS. If you still need more RAM, then go for it.
I have an HP a6120n running Vista (plan to upgrade to 7 soon). This came with 2 Gb or RAM, I assume in two 1 Gb DDR2-SDRAM modules. Can I add just one more 1 Gb module, to make 3 Gb, or do I have to replace them in pairs?