Exchange 2000 Public Folders size

My Exchange 2000 Public Folders have grown incredibly in size and I can’t see why. I have tried the all the obvious settings and limits, backup etc but to no avail. The wierd thing is that through the Windows Explorer Window the file Pub1.edb is showing (1.5GB) far greater than what the Exchange manager shows me (about 200MB, when you add the sizes of each folder up). Why is this space taken up? I am desperate because my disc is almost full. Therefore 200 Points.