Yes, this applet could be modified to process all the messages in a given folder. You would probably need to select the message you wanted to save, then use the Client.ClientState.SelectedMessages to access each selected message in tern. For example:
iCount = Client.ClientState.SelectedMessages.Count
gives you the number of selected messages. You can then access each message by:
Set Msg = Client.ClientState.SelectedMessages.Item(x)
where x is the index value of the message you wish to access.
We have also created a commercial applet that saves messages, including attachments, to a single file. This applet can process all messages in a given folder. If you would be interested in trialing this applet, please send an email to firstname.lastname@example.org.