try this..
DECLARE @Start_Time DATETIME, @End_Time DATETIME
SET @Start_Time = CONVERT(DATETIME,'08:00:00',103)
SET @End_Time = CONVERT(DATETIME,'16:00:00',103)
WHILE(@Start_Time <= @End_Time)
BEGIN
SELECT CONVERT(VARCHAR(8),@Start_Time,108)
SET @Start_Time = (SELECT DATEADD(minute,30,@Start_Time))
END
hope this helps...