Overriding Emacs 23 font substitutions

I use emacs with org-mode and other packages that assume all characters have the same width. This was not problematic until I started using Emacs 23 (on Mac and Linux) instead of Carbon Emacs. Now many non-ASCII characters (such as the phonetic characters in 0250–02AF) are rendered with a different font with different metrics. I would like to force emacs to render these characters with the same font as ASCII characters, e.g. DejaVu Sans Mono 10. How can this be achieved? Where is the d开发者_开发技巧ocumentation relating to emacs fonts in never versions located?

Try

(set-fontset-font
 nil '(#x0250 . #x02af) (font-spec :family "DejaVu Sans Mono"))

You can move the cursor (point) over the phonetic character and do a C-u C-x = to run some version of what-cursor-position. This will open another buffer containing information about what is under the cursor - including a line containing face and a descriptionof what face is used. Remeber the name of the face used.

Then, call M-x customize-face and enter the remembered used face and customize it to your needs.