Many of my text blocks are in Helvetica, which does not present well on a windows client. Since Windows machines come with Arial installed, I'd like to do a global change of all my Helvetica text to Arial. Is it possible to change a font across all layouts in a database? (Not referring to field fonts)
Not really, you can enter layout mode and go from layout to layout using your system's keyboard shortcut to select all, then change the font. That may or may not be useful to you depending on whether you want all objects (incuding buttons) to have the same font or not.