Here's some ASP code:
' WORK WITH STORED PROCEDURE PARAMETERS
' - get the database's Stored Procedure Parameters
' Create a variable and point it to the Stored Procedure Parameter
' in the report
set StoredProcParamCollection = Session("oRpt"

.ParameterFields
' - get the specific Store Procedure Parameter
' Create a variable and point it to the specific stored procedure
' that we want to work on
Set ThisParam = StoredProcParamCollection.item(1)
Set ThisParam2 = StoredProcParamCollection.item(2)
Set ThisParam3 = StoredProcParamCollection.item(3)
' - save the new value to the Stored Proc Param
' Create a variable and store the new value for the Stored Procedure
' in it
NewParamValue = "10"
NewParamValue2 = "50"
NewParamValue3 = ("'"&a&"'"
' Save the new value for the Stored Procedure in the Store Procedure
ThisParam.SetCurrentValue cint(NewParamValue), 7
ThisParam2.SetCurrentValue cint(NewParamValue2), 7
ThisParam3.SetCurrentValue cstr(NewParamValue3), 12