Timeout ASP0113 Error

Hi All,
I have an ASP application which is parameter driven.
The query below is generated for one of the reports. If the user selects a small subset of records i.e the WHERE has another clause, the results are returned within a matter of seconds. However, if the user wants ALL records within the dates - as given by the query below, I get a timeout error.
Is there another/better way to write this query?

Here is the SQL statement:
SELECT left(ExportData.dbo.tblWeeklySales.wsrCusNum,5) AS AccountNo,
ExportData.dbo.tblWeeklySales.wsrCusName as Client ,
SUM ( CASE WHEN DATEPART(yy,ExportData.dbo.tblWeeklySales.wsrWERun) = 2002
THEN ExportData.dbo.tblWeeklySales.wsrSales ELSE 0 END) AS Turnover2002,
SUM ( CASE WHEN DATEPART(yy,ExportData.dbo.tblWeeklySales.wsrWERun) = 2003
THEN ExportData.dbo.tblWeeklySales.wsrSales ELSE 0 END ) AS Turnover2003,

SUM ( CASE WHEN DATEPART(yy,ExportData.dbo.tblWeeklySales.wsrWERun) = 2002 then ExportData.dbo.tblWeeklySales.wsrProfit ELSE 0 END) AS Profit2002,

SUM ( CASE WHEN DATEPART(yy,ExportData.dbo.tblWeeklySales.wsrWERun) = 2003
then ExportData.dbo.tblWeeklySales.wsrProfit ELSE 0 END) AS Profit2003

FROM UserID2.dbo.tblBranch
INNER JOIN ExportData.dbo.tblWeeklySales
ON RIGHT(USERID2.dbo.tblBranch.brnBranchNumber, 3) = RIGHT(ExportData.dbo.tblWeeklySales.wsrCusBrn, 3)
WHERE (DatePart(m,ExportData.dbo.tblWeeklySales.wsrWERun) >= 1 AND DatePart(m,ExportData.dbo.tblWeeklySales.wsrWERun) <= 1)AND (DATEPART(yy,ExportData.dbo.tblWeeklySales.wsrWERun) < = 2003)AND (DATEPART(yy,ExportData.dbo.tblWeeklySales.wsrWERun) > = 2002)GROUP BY left(ExportData.dbo.tblWeeklySales.wsrCusNum,5), ExportData.dbo.tblWeeklySales.wsrCusName ORDER BY left(ExportData.dbo.tblWeeklySales.wsrCusNum,5) asc

TIA
Jackie