Note: I'm just your average Word user & I don't know what
version you're using but...
In Word 2002 the Find option has a tickbox for 'Highlight
all items found in".
If you tick this you can choose "Text boxes in main
document".
Assuming all text boxes have something in them you can
search for a space, or 'any character' under special
characters - ^?
Does this help??
Cheers
Caroline.
Susan pointed out:
This finds only inline graphics, which do not (usually) include text boxes.
Steve suggested: