Well right away i can see that you have Media Center running. (EHTray) That is where part of the cached memory is and why it isnt free.
I see Avast is also open. The GUI component. Flash Utility, Media Center Stats, XBOX Stat. The Media Center would be the biggest hog of the memory on why it is cached and not shown as free.
If you shut down Media Center you should see a drop in that number along with Free going up.
But according to the stuff i see you are in no real issue with memory. You are really only using 1.28GB of the 4GB you have. The rest is used by Super Fetch and cached.
Hope that better explains some stuff for ya.