IMO..there io little point in paying attention to RAM usage
if there are no problems. Those RAM states are useful only when there is a problem and you don't seem to have one.
Example: I have 4GB installed on this system, I am currently in Win XP. Task Manager tells me that I have 3.4GB installed and 2.7GB available...none of that is important, since I know that I have 4GB installed and I don't care how much is "available" or "used" at any given point in time...unless I develop a problem. RAM is not money, it's meant to be used...not saved for a rainy day
. If you install 4GB, Windows will use it as efficiently as possible and you can forget about Task Manager RAM figures...until you have a problem.
You should have 4GB installed at a minimum for Win 7, whether 32-bit or 64-bit. If 64-bit Windows, then you could install more but I don't reommend it (since you got along with 2GB before) and you won't gain much.