you know about Synergy? i'm not sure what you know about it, but you can't change type with it. as far as i know it just adds a iTunes controller to your menbar...
you're looking for Slik, a haxie by Unsanity.com. you can change the system-wide font or i think you can specify to only change a font of a specific app.
if you're looking for info about custimizing OS X you should check out the GUI forums at MacNN, or also the Mac forums at NeoWin. but it's good to ask here as well, we do know about these things you know.
is that what you're looking for? just ask if you need anything else.