Since the inbuilt Font Dialog returns a \'Not a True Type Font\' Exception on selecting a Non True Type Font, I\'m trying to create a Custom Font Dialog using Font-families
http://www.developerfusion.com/code/254/determine-if-a-font-is-truetype/ has some VB code to determine whether a font is a TT font. All it really does is call some Win32 API functions and examines the results.
There may be some fonts that appear to be TT but aren't, even when examined with the Win32 API (which the FontDialog is probably doing anyway). If Win32 doesn't fix your problem, then probably the only way to find out if a font is invalid is to check for an exception.