How can i know the relationship in the database in sql server 2008?
When I have encountered similar problems to this in the past, I have used the query that marc_s provides here: Know relationships between all the tables of database in SQL Server

It should give you a good place to start?

Here it is replicated in case the other thread is removed in the future (credit - marc_s):

SELECT
fk.name 'FK Name',
tp.name 'Parent table',
cp.name, cp.column_id,
tr.name 'Refrenced table',
cr.name, cr.column_id
FROM 
sys.foreign_keys fk
INNER JOIN 
sys.tables tp ON fk.parent_object_id = tp.object_id
INNER JOIN 
sys.tables tr ON fk.referenced_object_id = tr.object_id
INNER JOIN 
sys.foreign_key_columns fkc ON fkc.constraint_object_id = fk.object_id
INNER JOIN 
sys.columns cp ON fkc.parent_column_id = cp.column_id AND fkc.parent_object_id =      cp.object_id
INNER JOIN 
sys.columns cr ON fkc.referenced_column_id = cr.column_id AND fkc.referenced_object_id = cr.object_id
ORDER BY
tp.name, cp.column_id