I'm one of the few Windows users in our office and had been searching for this utility for some time to help report CSS bugs to developers internally.
Finally, got lucky today while Googling, and reached http://www.kabatology.com/01/03/take-your-screenshots-on-windows-with-lightscreen/.
You could download Lightscreen from http://www.qt-apps.org/content/show.php/Lightscreen?content=72757
It does not have features to highlight areas you want to draw someone's attention to.