I'm not sure there's a global setting for the entire suite you can set. I know Managed Preferences (MCX) has a an item in the templates in the JSS for Outlook, called "HTML Web Kit Standard Font" You can set that to your Arial font and it should set Outlook to use it. Or if you're not using MCX, you'd have to drop the settings into a Config profile or otherwise script it with defaults or PlistBuddy.
However, I don't see any equivalent settings for Word, Excel, etc. Maybe its under a different obscure name, but I took a quick look though Word's prefs and I don't even see a place to set a default font in the GUI. Is there one?
Also keep in mind the above Outlook setting can't be enforced. Its a user side setting. You can set it once or at every login, but no way to lock it in that I'm aware of.
