making index.php display most recent entry in specific category as default

hi — i’m setting up a site which has a newsletter as well as various other categories (i.e. each newletter will be a single post into a specific category). when visitors first access the site, i want the first thing they se to be the most recent post *in the newsletter category* rather than the most recent post over all — i.e. something like

http://my.site.tld/index.php?cat=1

as the default view. what’s the tidiest way to do this?
thanks