Jakub Kazecki posted a handy tip in our newsgroups which enables posting to MovableType directly from FeedDemon.
First, select Tools > Blog this News Item > Configure Blog Publishing Tools, then click the "Add" button and enter this as the command line:
http://www.myblog.com/cgi-bin/mt.cgi?
is_bm=1&bm_show=&__mode=view&_type=entry
&title=$ITEM_TITLE$
&link_title=$ITEM_TITLE$&link_href=$ITEM_LINK$
&text=$ITEM_DESCRIPTION$
Where 'www.myblog.com/cgi-bin' is the URL of your MT installation.
After doing this, you'll be able to right click on a news item and select "Blog This News Item" to post to your MovableType blog directly from FeedDemon.