Row offset values

What is the fastest way to select a value offset by n rows from the start row? I used to use a cursor with FETCH ABSOLUTE in Sybase SQLAnywhere, but this is incredibly slow in SQL Server. Here's the current function I'm using:

FUNCTION dbo.TradingDaysBack ( @.ItemID int, @.FromDate smalldatetime, @.DaysBack int )
RETURNS smalldatetime
AS
BEGIN
declare @.BackDay int
declare @.OADay int
set @.OADay = dbo.GetOADate(@.FromDate)
declare curDaysBack cursor scroll for
select OADate
from Data_Daily
where ItemID = @.ItemID and OADate <= @.OADay
order by OADate desc

open curDaysBack
fetch absolute @.DaysBack
from curDaysBack
into @.BackDay

close curDaysBack
deallocate curDaysBack

if @.BackDay is null
begin
set @.BackDay= ( select Min(OADate) from Data_Daily where ItemID = @.ItemID and OADate <= @.OADay )
end

RETURN convert(smalldatetime, @.BackDay)

END

The idea is to get the date n rows of data back from the starting date (i.e. 30 trading days back from 12/1/2003). Any ideas?DATEDIFF?

You know your example is only selecting 1 row....|||It can't be DateDiff, because not every day is a trading day, obviously. I need to go back n trading days, meaning entries for the given ticker between two dates. And yes, it is only selecting one row, which is the idea.sql