I'm a newbie to Flash, but I *think* it works something like this (please correct me if I'm wrong). You add hyperlinks to your text file like so:
Come and see the <a href="http://www.cnn.com">CNN website</a>.
Now when you read in your text file you have to make sure the dynamic text field that will hold the text is allowed to display as HTML. To do this I use this AS code:
myTextBlock.html = true;
I think that if add links to your text file and then declare the text field HTML endabled, you should be able to add your links. You might want to add a style sheet as well so that you have control over how the text appears.