You could open Resource Monitor to see exactly how your RAM is being allocated. Resource Monitor
Windows 7 does a better job of allocating RAM than previous versions of Windows. As a general rule, you should not have any available RAM (or at least very little). Available RAM is wasted RAM. You paid for all of it and you really don't want to see any of it wasted. Windows 7 works hard to keep all your RAM working for you all the time, for example using it for cache if your apps don't need it, then taking it back again if your apps need it later. This is a good feature of Windows 7, not bad.
You could also run the free Process Monitor to get a better idea of what's using your RAM. Don't even have to install it. You can run it from the live link at the bottom of the page (run process monitor now.) Process Monitor