Maybe you get some useful information about what locks the table using sys.dm_tran_locks (http://msdn.microsoft.com/en-us/library/ms190345%28v=sql.90%29.aspx)

There are some other Transaction Related Dynamic Management Views and Functions that might help you: http://msdn.microsoft.com/en-us/library/ms178621%28v=sql.90%29.aspx