This is what I got to work:
IF OBJECT_ID('T1') IS NOT NULL
DROP TABLE T1;
GO
CREATE TABLE T1 (id int PRIMARY KEY, timestamp);
GO
INSERT INTO T1(id) VALUES (1);
GO
declare @v as table ([timestamp] varbinary) --timestamp;
INSERT INTO T1(id)
OUTPUT inserted.[timestamp] into @v
VALUES (10);
select * from @v
One thing you need to realize is a timestamp field cannot be manually populated. So you must use some other type in your output table. ANd BTW timestamp is deprecated, I would not use it in new development at all. Use rowversion instead. And timestamp doesn't mean it will be a date for those who think it should be like the ANSII Standard, IN SQL Server it is not a date or convertable to a date.