I'm still playing around with this myself.  I've found if you go into SkinStudio7, choose change skin fonts-->go to the drop down menu and choose show me the skin defined system fonts and play around with the sizes that will change some of the fonts, but you might have to reboot in order to see all the places that are changed.

OH!  I think I might know what you could do.  If you open up Windowblinds 7, down at the bottom there is a Fonts tab -- you can choose what font you want, and you can make it bigger or smaller. Or, to change the Windows 7 font, system wide, you can follow the instructions in this article:  http://mintywhite.com/windows-7/7customization/windows-seven-7-increase-screen-font-size-how-to/

OK, I think I understand what you're asking better now. 

I found these instructions and it worked on my computer, which is Windows 7 Home Premium, 64 bit. 

http://www.sevenforums.com/tutorials/1175-fonts-change.html