That Text and font Is in the aero.msstyle in C/Windows/Resources/Themes I have WSB and I can tell you the text and font tooltips on the taskbar can be changed, the tooltips when you hover over a file or folder in Windows Explorer the text color can be changed and if you want the font changed there it will change the font in Windows Explorer and in the start menu to.
If you are using the default aero theme I can change that for you.
If you are using a custom theme you will need to ask the
theme maker. It's not cool to change someone else work.
You will need to do 1 of these 2 ways of Enabling custom themes for it to work. Enabling Custom Themes - Windows 7
Or Theme - How to Apply Custom Themes
Let me know.