create a parameter field in the report. I hope its there in CR 6.
And I guess the you are using the Crystal Report viewer control , not Crystal Report Control.
to pass the value you can use like this
Code:
Dim myreport As CRAXDRT.Report
    myreport.ParameterFields(1).AddCurrentValue "test"
remeber the index for the parameterFields collection should match the order of parameters in the report.
This I tried in CR 8, I hope its same for CR6