Upgrading your laptop memory is the easiest way to get a real and relatively cheap performance boost.
If you're struggling along with a system running 1GB or less then dropping in extra memory will help it run a lot more smoothly and finish tasks faster.
The reason is that extra memory helps cut-down unnecessary hard drive access. When Windows runs out of real-memory to store application and system data it has to resort to temporarily using the hard drive.
This takes hundreds of times longer and is a key reason you can end up sat there twiddling your thumbs when switching between tasks.