1) you can use the back compression method of sql server 2008

2) is the database is in full recovery mode ?

3) if the vendors request is one time and you can afford then you can go for dbcc shrink database follwed by index rebuild BUT Its usually a pretty bad practice for most databases. The database needs a certain amount of free space to be able to function under regular DML so removing all the free space is just going to cause it to grow again. Also, the data move operation does not 'intelligently' place the data lower in the file, it just moves it to the first free space it can find - this causes index fragmentation and can lower performance.