Sql Server huge tables with no rows

Rebuild all indexes on the tables, including the clustered index. From Books Online:

Rebuilding an index drops and re-creates the index. This removes fragmentation, reclaims disk space by compacting the pages based on the specified or existing fill factor setting, and reorders the index rows in contiguous pages.

Something like:

ALTER INDEX ALL ON [lc_db_user].[JMS_MESSAGES] REBUILD

DBCC SHRINKDATABASE or (more preferred) DBCC SHRINKFILE will only do something if the space has actually been freed from the table itself. Also please make sure you are familiar with the issues associated with shrinking database files. The executive summary: NEVER use auto-shrink, only shrink files when necessary, and always follow up with a full reindex to defragment all the indexes you've just fragmented.

Another way to deal with that kind of problem is to use the TRUNCATE TABLE statement:

TRUNCATE TABLE [lc_db_usr].[JMS_MESSAGES]

This will, however, only work on tables not referenced by a FOREIGN KEY constraint.

For more details: http://msdn.microsoft.com/en-us/library/ms177570.aspx