Unless some has that exact theme it may be hard for anyone to give an easy answer.
You can use view page source when viewing your site to find a class that wraps the content that you wish to change the font for, and then add that class to the bottom of the css file for your theme. I usually add a comment line like "begin site specific theme changes", so that if something else isn't behaving correctly later I can comment out my entire section to see if it is related. A change lower in the file in css always overrides a prior setting for the same class. It may also be that the class you add has never been specifically previously defined, in that case it's possible the class will work for the change, but if it doesn't then try to find a more specific class that wraps your content as there may be several. A tool such as firebug can also be very useful in determining what class to override.
It would be helpful when posting a question like this to include the domain name, as it may provide more specific answers.[hr]
FWIW, this forum is small enough cross posting does little good, and in fact can make answers more confusing for a user using search later. I'm sure when andrewf come through he will either combine your two threads or delete the other if it still has no replies.