Separate posts by days

Any WP PHP gurus, this may be for you. Trying to hack the WP source to get daily posts to be separated by some type of demarcation (probably an <hr />). I want this to happen in between days. So when I put up say five posts today, tomorrow when I post the php (or Javascript?) will automatically insert a single <hr /> tag between today’s posts and yesterday’s, etc. Don’t know how else to describe this. Any help/code/links would be sweet.