Overclocking can be worth it, but in your case it wouldn't be because of your GPU - which I believe is an integrated graphics card.
Overclocking will void any warranty you have.
You can overclock your CPU but I can't tell you if it would be worth it or not. The two major dangers with overclocking are heat and overclocking too much too quickly. Overclocking a component causes it to work harder, which means it would generate more heat and require more power.. so buying an aftermarket cooler and ensuring your PSU has the strength to power the overclock is often suggested. Here's a link to another forum about overclocking your CPU.
http://www.sevenforums.com/pc-custom-builds-overclocking/103420-how-overclock-intel-core-2-duo-e6750-3-0ghz-2.html
and here's another link that explains overclocking:
http://lifehacker.com/5580998/a-beginners-guide-to-overclocking-your-intel-processor
Overclocking the GPU is relatively easier to do and you can do it with programs like MSI Afterburner, EVGA Precision, ATI Tool, and RivaTuner.. although MSI Afterburner is probably the best program to do it with; overclocking any component is theoretically the same process: increasing clock speeds and voltages to higher (but stable) levels -
doing so in very small increments at a time.
However, your GPU is an integrated card it seems, so, even if you overclock your CPU, your PC will still be limited by your GPU's graphical abilities.. or lack of.
But, if you're overclocking to increase performance in some specific CPU intensive programs that don't use > 2GB of RAM then, it
may be worth it.