Using the DataSourceConnection Class for Database Logon
Basically you need to set the logon information to get the prompt to not appear, even if you haven't password protected it. I believe your code would need to look something like this:
Dim rep As New ReportDocument
.DataSourceConnections.Item(0).SetConnection(strServerName, strDatabase, strUser, strPassword)
CrystalReportViewer1.ReportSource = rep
Hope this helps.