When I make a block in the Drupal admin area I sometimes want to run code in that block but not use the Drupal block edit area to do it.
This is how I over write the block.
Open the block.tpl.php
Then rename it as block-block-#.tpl.php
The # is the number of the block you are going to control this way.
You can find that out by putting in

   print_r($block); 

to the absolute top of block.tpl.php and see what it returns for delta for where the block is you want to control
Now you are done.
Anything you put in there will control that blocks output
Block assign makes some later work easier
http://drupal.org/project/block_assign