With PowerPoint 2008, you're able to change the default numbering
and bullet styles for text in the placeholders.
Click on View - Slide Master, select the slide layout that you
want to change, and edit the styles on the text placeholders
as appropriate. The styles on placeholders of any new slides
you create with this layout will change along with the master.
However, if you have deliberately made any changes to the
placeholder styles in Normal view on specific slides,
those styles should remain as you set them.
However, there doesn't seem to be a way to change the default
numbering and bullet scheme for text boxes (not placeholders,
but text boxes drawn using the text box tool). It's
understandable, since PowerPoint has no way of knowing
what you're going to type into individual text boxes, nor
of the levels of information and styles you're going to
apply. (With placeholders, you set the style for each
outline level of information, and PowerPoint can easily
follow that.)
The best workaround is to create a text box with the
styles, bullets and numbering that you prefer, and then
simply copy that text box as your template to use over
and over. The Formatting palette, Bullets and Numbering
section should help you in quickly selecting numbering
and bullet styles as well for your "template" text box.
Jeff