If I understand you correctly this can be achieved using cursors.
Add a cursor to the graph (this can be done through the cursor tab in the properties page). Set the crosshair style to Major X & Major Y. Set the color to whatever you want it to be. Set the Point style to Cross. UNCHECK "enabled" so that the cursors cannot be dragged.
After you send the data to the graph simply add this line of code.
CWGraph1.Cursors(1).SetPosition 0, 0
The cursors should now represent the x and y axis.
Attached is a simple example.
Hope this is answers your question.
Kevin