You don't need more memory if you can do what you need to do. You will not get over 3-3.5 gb without going to a 64 bit OS, depending on your video card. As long as you have a paging file, then the virtual memory will suffice. Unless your computer gets too slow to do what you want, don't worry about the message.
You do probably have too many unnecessary apps that are using memory though -- look through your services and figure out what you really need, many are probably just available to check for updates and other crap uses. email and internet do not require much, but every time you install something it often brings along crapware.