That's normal, the information there isn't perfectly accurate and doesn't account for all of the memory that's being used. But those numbers are absolutely normal for a healthy 4GB system.
Task Manager counts differently, the rest of the memory is being reserved for several purposes. Hardware needs some, and the OS will fetch and reserve for performance.
That's keeping it real basic and simple. If you want a more expert explanation, you should be able to find tons of posts regarding this just by searching. It's been discussed here many many times, in great detail.