Isn't it a lot simpler to use a LED driver such as this one: http://nwazet.com/leddriver ? Less than $9 and able to drive a 8x8 matrix. I have a post on my blog showing how to control an 8x8 matrix with a single shift register: http://weblogs.asp.net/bleroy/archive/2010/12/06/displaying-an-image-on-a-led-matrix-with-a-netduino.aspx but doing it with a LED driver is a lot cleaner: http://weblogs.asp.net/bleroy/archive/2011/03/24/driving-a-led-matrix-from-a-netduino-one-more-time-the-right-way.aspx