Damaged memory?

Hi. A few months back, I upgraded my bottom of the line Macbook to 2GB of memory, and it rocked, as the activity monitor was always atleast halfway green on the memory pie. Over the past few days, however, that green has been replaced with blue, designating inactive. Now, I understand what inactive memory is, but my problem is that I look at what's using memory, and all of it added up only equals about 500 MB. Is my memory damaged, or is there something else going on?