Hi,
Been researching on this, and I'm afraid it will not be implemented.
If you create a new PST file, only "deleted items" and "search folders" will be created by default. Desktask relies on a Outlook function that gets de default calendar and default tasks folder. In other PST's there is no default calendar and default tasks folder, thus creating a problem. So at the time being support for additional folders and/or other PST Files will not be available.
We're sorry for this.
André Santos Carthago Software Support
http://www.carthagosoft.net