Solution: in network tracks mode, select a range of objects and Edit > Copy these. The clipboard now contains GPX fragments of these items. You can paste that into a second TrailRunner document or into any text file.
Tip: you can also use this technique to give parts of your network of tracks to a friend for that he/she can import these segments.
Solution: Services like http://twitterfeed.com can publish RSS Feeds to your twitter account. TrailRunner also published an RSS feed along with your weblog. You'll find the feed here: http://web.me.com/