Example of how to set parameters via code behind for an SSRS rdl report

        ReportExecutionService rs = new ReportExecutionService();
        rs.Credentials = System.Net.CredentialCache.DefaultCredentials;
        rs.Url = "http://ServerName/reportserver/ReportExecution2005.asmx";

        ExecutionInfo execInfo = new ExecutionInfo();
        ExecutionHeader execHeader = new ExecutionHeader();

        rs.ExecutionHeaderValue = execHeader;

        execInfo = rs.LoadReport(reportPath, historyID);
        //execInfo.Parameters[0].
        ParameterValue prmCompanyID_1 = new ParameterValue();
        prmCompanyID_1.Name = "iCompanyID";
        prmCompanyID_1.Value = "276";

        ParameterValue prmCompanyID_2 = new ParameterValue();
        prmCompanyID_2.Name = "CompanyID";
        prmCompanyID_2.Value = "276";

        ParameterValue prmProdMonth = new ParameterValue();
        prmProdMonth.Name = "ProdMonth";
        prmProdMonth.Value = "12";

        ParameterValue prmProdYear = new ParameterValue();
        prmProdYear.Name = "ProdYear";
        prmProdYear.Value = "2010";

        ParameterValue[] prmList = new ParameterValue[4] { prmCompanyID_1, prmCompanyID_2, prmProdMonth, prmProdYear };

        rs.SetExecutionParameters(prmList, "en-us");