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
fromData_Daily
whereItemID = @ItemID and OADate <= @OADay
order byOADate 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?