A "Delete from [table]" command for each of your tables is all you need.
If you have foreign keys you will need to delete the child table before the parent tables can be emptied.
You can get some scripts to output all the tables etc, but I find it useful to do this myself, if I dont know the structure will enough, it is a good learning exercise.
You'll get a relational integrity error if you do not execute the deletes in the proper order, but all you need to do to fix it is change the order of your Delete statements.
http://www.db-pros.com