Retrieving Data Based On Value In A Field

Hi I hop i make sense with this, i have a page where you can update a products price based on the year, so for instance some products will still have prices set in 2007, while some may have prices which will be set in 2008, what i am trying to do is if the price has been set in 2008 it shows this value. The fields in the table which control the values are Rate(controls 2007), and Rate2007Period2. What i am trying to do is if Rate2007Period2 is null or 0, then display the 2007 rate, and if Rate2007Period2 is greater than 0 then display that value. Here is the view which displays the rates;

SELECT     dbo.tblRateSchedule.MA_Code, dbo.tblRateSchedule.SOR_Code, dbo.tblRateSchedule.DESCRIPTION, dbo.tblRateSchedule.SWT,
                      dbo.tblRateSchedule.Rate, dbo.tblRateSchedule.Tstamp, dbo.tblRateSchedule.RateSchedule_ID, dbo.tblRateSchedule.RateScheduleUnit_ID,
                      dbo.tblRateSchedule.RateScheduleType_ID, dbo.tblRateSchedule.WorkType_ID, dbo.tblRateScheduleUnit.Unit,
                      dbo.tblWorkType.Work_Type_Description, dbo.tblRateScheduleType.Type, dbo.tblRateSchedule.Work_Type_Description AS Expr1,
                      dbo.tblRateSchedule.Rate_Active, dbo.tblHistoricalRateSchedule.Rate2006Period1, dbo.tblHistoricalRateSchedule.Rate2007Period1,
                      dbo.tblHistoricalRateSchedule.Rate2007Period2
FROM         dbo.tblRateSchedule INNER JOIN
                      dbo.tblHistoricalRateSchedule ON dbo.tblRateSchedule.MA_Code = dbo.tblHistoricalRateSchedule.MA_Code LEFT OUTER JOIN
                      dbo.tblRateScheduleType ON dbo.tblRateSchedule.RateScheduleType_ID = dbo.tblRateScheduleType.RateScheduleType_ID LEFT OUTER JOIN
                      dbo.tblWorkType ON dbo.tblRateSchedule.WorkType_ID = dbo.tblWorkType.WorkType_ID LEFT OUTER JOIN
                      dbo.tblRateScheduleUnit ON dbo.tblRateSchedule.RateScheduleUnit_ID = dbo.tblRateScheduleUnit.RateScheduleUnit_ID
WHERE     (dbo.tblRateSchedule.Rate_Active = '1')