put your insert inside of an If not Exists statement
Dim strSQL As String = "If Not Exists (" & _
"Select * From tblDetail " & _
"Where PersonId = " & strPersonID & ")" & _
"INSERT INTO tblDetail VALUES('" & strPersonID _
& "','" & strForename & "','" & strSurname &
"','" & strDateOfBirth & "'," &
strCurrentlyWith & ",'" & strConditions & "')"