Windows ME System Resources

The computer has 512 memory available.
Two Gig Pentium running Windows ME
However when a program is closed the memory is not released. A message comes up saying “System Resources are dangerously low.. close a few windows/programs and try again” All visible programs will be closed by this time (except operating system) and still get this message. The only way (so far) to clear up memory is to restart machine. Any ideas?

Thanks