OnClick Or OnMouseOver - Pulling Information From An Element Whose Id = 27...which Is Not What I'd Like?

I use mostly PHP with my office's website as it usually requires some interaction with the server. However, i would like to do something that does not,and figured JS should be able to take care of it.What i would like to do seems rather simple:I have a calendar. I would it to do one of two things:

1. Using onclick, when the user clicks on a date, i would like it to print something underneath the calendar. Similar to an error message that shows up on a login form if you type something wrong in a field using PHP (if(isset($whatever))).

2. Or using onMouseover, if the user hovers over a date that i have something special scheduled, i want a message to either pop up (alert()) or similar to #1, show up below the calendar.

While fiddling with it this afternoon i figured i was close, but i am missing something...

<td><a href="#" onclick="document.getElementById("27").innerHTML='President's Day'; return false;">27</a></td>

But this seems to be pulling information from an element whose id = 27...which is not what i'd like..