You can use something like the following to get previous years:
Add month & date selection box's and you can compare as many different time periods as needed.
So if you select 2010 as your current Fiscal_Year, the above statement will display data for 2009. If you have no Fiscal_Year selected it will use max - 1, or 2010.
Further you can combine them in your expression to just show you the change:
In your load script identify the day of the month somewhere in your tables (1-31) and the name of the month (Jan-Dec) then add those fields into a listbox or multi-box which the users can use to select a specific month or day to compare year over year.
year(SalesDate) as SalesYear,
quarter(SalesDate) as SalesQtr,
month(SalesDate) as SalesMonth,
weekday(SalesDate) as SalesDay,
day(SalesDate) as SalesDayNum,
Putting all of the above fields into listbox's will allow the users to compare virtually any year over year period they wish.
Then change the set statement from earlier to read
When a user selects 2009 from the SalesYear listbox, the formulas will look at 2008 & 2009.
When they then select 2 from the SalesQtr listbox the formulas will compare Q2 2008 to Q2 2009...
Hope that helps!