Defragging Exchange servers

I have an exchange server with Win NT 4.0 that was originally installed in drive c:\, then the DB was moved to d:\ with the optimizer. Now the DB has 3 GB of space but it?s supposed to have 2.0 GB of free space. I need to defrag the DB at the exchange level and at the OS level but Microsoft doesn?t recommend defragging the NT servers. What should I do?