There isn't really too much of a stock way of having a global announcement display for all but a specific forum. You'd probably have to add a check for the "$Board" variable on the bit of code for announcements from scripts/postlist.inc.php.
Please note that modifying your stock code can introduce bugs into your copy of the software and that
UBBCentral cannot support modifications performed to stock code as your modifications are not their code to support.
