Is this database upgraded from SQL 2000 version?
What is the log file size?
Please run this query and post the results here:
select name, type_desc, size/128 'Size(MB)', FILEPROPERTY(name, 'SpaceUsed') / 128 'SpaceUsed(MB)'
You can the reduce the MDF file size by using DBCC SHRINKFILE. But set the file size to appropriate size.
Unallocated space = 'Space in the database that has not been reserved for database objects.' (from BOL)