1.5 GB available is about average for windows 7 that has been installed for a while. You can't just shut down anything you want in the processes tab or you can have that issue. What I meant for you to do was look and see what programs are using the ram. Research them and see if they need to be running. Some process need to run others are process for other programs that start automatically, like Adobe, mouse diver software ect. Everything in your tool tray has a process that could be sapping your available ram.
Win Vista and Win 7 both use about 2 GB of ram just for the OS. Then any program running on top of that take some ram. As you can see this could add up quickly. From the numbers you provided your system is right around where it...