You can see this in action at Not Far North.
First, you need the glx_if plugin installed.
put this in your "article" page template:
/> dl> </txp:glx_if_section_frontpage> <txp:if_individual_article> <txp:article /> txp:if_individual_article>
If you were attentive, you see that we also need an article_archive form. Create that form and put this in it:
<txp:if_different> <dt><txp:posted format="%B %Y" />dt> </txp:if_different> <dd><txp:permlink><txp:title />txp:permlink>
Now, "yoursite.com/article" will display a list of articles broken out by month, and "yoursite.com/article/2/helloworld" will display only that article using the "default" form.
To handle category listings, install the upm_category_title plugin and add this to your front page ("default") template:
<txp:glx_if_category_list> <h2>Articles in <txp:upm_category_title />h2> article/">View all articles
"article" form="article_archive" /> "2" form="article_newest" />
Note that using the above bit of code requires you to modify the glx_if plugin a bit - more about that in another snippet (it's really easy).