The order in which messages are added to a conversation is specified in the Options Manager in the "Order of Items" section (found under the Conv/Msg tab in version 4.0).

By default, new messages are added to the bottom of a conversation. To cause new messages to be added to the top, simply check the box in the "Add new messages to top" column next to the topic(s) where you want this to occur.

For more information, consult the administration instructions for Options Manager, available within your Discus distribution through the administration program.