Memory Information gives you information about how much memory your rack file is consuming and how much spare memory you have. If the required memory is greater than the Threshold, a warning will be displayed when the rack is loaded.
On 32 bit versions of Windows with 4GB of RAM, it is normal to see usable memory of only about 1500MB or so on an empty rack. The reason for this is that 32 bit Windows by default give each application only 2GB of memory. It is not a problem with Forte. About 500MB of that is loaded with the application and a large number of Windows DLL components. See this to take advantage of a Windows configuration change that makes more memory available to Forte.