I doubt you are utilizing even 2GB of RAM. You could safely experiment with a 1GB RAM drive now (leaving 3GB for the system). Here is a program that will let you create one up to 4GB for free. I've used it for a few years and it works great. I'm sure you'll be surprised at how easy it is. Make sure to run crystal disk or something on your HDD and then compare it to the RAM drive!
Here's my netbook's HDD and RAM drive:
Quite an improvement, but still not as fast as a good SSD.