Linking section box to many categories

[gtotino]

I have read this http://www.studiopress.com/support/v...x#p20428%20%20 post and it was very helpful in understanding how to pull more than one category in one section box.

Now, I would like to know how to have the link at the bottom of the section box, the one that reads "Read more posts from this category", opening an archive page listing posts from all the categories pulled into the section box.

Many thanks in advance as usual! :)

PS
For next time: how could I have avoided putting the entire link here in the post? I could not figure out how to get the word "this" linked to the URL. Can you tell me please?