X and Fluxbox :: Default Font for Menus, Dialogs?

I posted a specific question about Sylpheed in the How To area, and then thought it might fit better here - sorry for the duplication.

Question: I note that many of the apps use a font for the menu bar and the drop down menus (File, Edit, etc.) that I find just too small. Is there some place in the configuration of the system where a "default font" is set for menus, dialogs, etc.? Is there any simple way to change this, so that the default font size is increased? Thanks!

original here.