to change the font on the tabs itself you will need to go where you save all the docks to apply them (i think its public documents) and open up the dock configuration file with a text editor eg notepad and from there you will have to type in the name of the font you wish that style to use
I'm not saying this won't work, I'm just asking WHY?!?
If you read replies 1 & 2, Cavan1 & I have given the easy answer--the answer which allows one to change the font, size and style; then change it again if they wish. No hard coding needed. 