You can either use CAST function, which is available fo SQL-Server down to MS SQL v7
SELECT * FROM TABLE_NAME WHERE CAST(mitarbeiterid AS varbinary(40)) = CAST('bbe' AS varbinary(40))
Or use the COLLATE function (available after MS SQL 2000) with an appropriate string pattern;
SELECT * FROM TABLE_NAME WHERE mitarbeiterid COLLATE Latin1_General_BIN LIKE '%[a-z]%'