>There are 30 tables with difference collations. How can i make them the same?

Collation is stored on a column level so you'll have to modifi all columns in question. You may also want to modify collation for a database itself to appropriate default collation.

ALTER DATABASE DatabaseName COLLATE CollationName
ALTER TABLE TableName 
    ALTER COLUMN ColumnName1 COLLATE CollationName
ALTER TABLE TableName 
    ALTER COLUMN ColumnName2 COLLATE CollationName
...

Chek also http://support.microsoft.com/kb/325335