Still not sure what the problem is... your example works just fine:
DECLARE @tbl TABLE
(
DATE DATETIME,
amount DECIMAL(10,2),
interest FLOAT
)
INSERT INTO @tbl
SELECT '2009-04-10 00:00:00.000', 450.00, 00.23 UNION ALL
SELECT '2009-04-10 00:00:00.000', 451.00, -1.20 UNION ALL
SELECT '2009-04-10 00:00:00.000', 460.00, 2.5
SELECT DATE, amount, interest FROM @tbl WHERE interest > 0
/* result set
dateamountinterest
2009-04-10 00:00:00.000450.000,23
2009-04-10 00:00:00.000460.002,5
*/