To disable the parameter prompt, you have to populate the parameters with a value prior to generating the report. Once CR sees that the parameter has data, it will use that data to create the report without prompting the user.
Use the SetParameterValue() method of the ReportDocument class to set the parameter. The first argument is the parameter name and the second is the parameter's value.
You need to set the paramters in your VB app. Any parameters you do not set will get prompted for.
If you are setting them but still getting prompted, make sure you are not using the Refresh method because that will cause the report to prompt for the parameters again. Same as in the Report Designer and you go to refresh the report you get prompted to use the current parameters or to discard them.
Hope this helps,