In iWeb, you can link text in your site to another webpage, to a file, or to an email message by selecting the text and selecting the "Enable as a hyperlink" checkbox in the Link Inspector.
However, if you link text to a file, the text will be replaced with the name of the file that the link points to.
For instance if you selected the text here from a sentence which reads "Download cupcake recipe here" and then linked it to a file called cupcake.rtf, the sentence will change to "Download cupcake recipe cupcake.rtf".
You can change the file name text by selecting the link (make sure the "Make all hyperlinks active" checkbox in the Link inspector is deselected) and adding new text in it's place.
This document will be updated as more information becomes available.