[Error: Irreparable invalid markup ('<style/css>') in entry. Owner must fix manually. Raw contents below.]
After your GLOBAL_HEAD tags and before your <style/css>, you should paste in the quick use code from the Google web fonts. Then in your <style/css>, use the following:
p table table td.caption {font-family:FONT NAME HERE;}
And of course you can add whatever other color and size specifications for your subject line like you would for the namefield.