Also, I am pretty sure that you do not need to do anything with the BIOS to get 1600mhz RAM chips up to 1600mhz. What is the speed on your current 2gb RAM though? If you currently have 1333mhz RAM, and you plug in 1600mhz RAM, you will probably have some issues.
The new stick would probably default to 1333MHz anyway. My 1600MHz (now OC'ed to 1866MHz) ran at 1333MHz and I had to enable XMP to change it to the manufacturers settings.
Also, I would not suggest mixing different types of RAM. Many cases have them not running well together and can cause issues. I would say it is best to get a whole new set.