Memory

Adding RAM is an easy way to boost performance, but first make sure the notebook's memory sockets are accessible. (They're usually under a panel on the bottom of the system.) Here's an easy way to determine how much you need:

512MB: Generally fine if you're running a Linux variant on something small like an EeePC, but really, this is far too little for today's uses.

1GB: Adequate for running a number programs at once, photo editing, and basic 3D gaming. Also the minimum required to run Vista.

2GB or more: Recommended! Good for 3D gaming, graphics work, and video editing, and will definitely give Vista a kick along. 2GB is a nice safe bet in terms of giving your laptop the flexibility it needs. If you hit the 4GB point, you'll need to run a 64-bit Operating System to take advantage of all of the memory -- a 32-bit one won't be able to access it all.