I Was bit struggling with this Problem.......
If u make a report in vb.net and display it using CrystalReport Viewer, then by default at runtime it prompts you for database password.
I tried to google it. but found no proper solution.
Finally a trick worked for me. so i thought of writing it down for all who are
struggling with the same problem.

Code:
Dim report As ReportDoc = New ReportDoc

 Dim crParameterDiscreteValue As CrystalDecisions.Shared.ParameterDiscreteValue

        Dim crParameterFieldDefinitions As ParameterFieldDefinitions

        Dim crParameterFieldLocation As ParameterFieldDefinition

        Dim crParameterValues As CrystalDecisions.Shared.ParameterValues

 crParameterFieldDefinitions = report.DataDefinition.ParameterFields



        '' Add a parameter value - START

        crParameterFieldLocation = crParameterFieldDefinitions.Item(0)

        crParameterValues = crParameterFieldLocation.CurrentValues

        crParameterDiscreteValue = New CrystalDecisions.Shared.ParameterDiscreteValue

        crParameterDiscreteValue.Value = Parameter1

        crParameterValues.Add(crParameterDiscreteValue)

        crParameterFieldLocation.ApplyCurrentValues(crParameterValues)

        report.SetParameterValue(0, Parameter1)

       crParameterFieldLocation.ApplyCurrentValues(crParameterValues)

       report.SetDatabaseLogon(DBUser, DBPass)       '***** DBUser  And DBPass are username and password of database

        rptviewer_1.ReportSource = report

Here, SetDatabaseLogon does the trick...
Hope It Helps to Someone...... !
Cheers !
-----------------------------------
Kedar Kulkarni