If the region code of the DVD is different than the region code on the DVD drive, the DVD drive's firmware will change to match the region code of your DVD. No changes to your computer are made.
Note that even external DVD drives are limited to the amount of region code changes they're allowed -- usually 5 -- before they're not allowed to change any more, and locked to one region code. It's for this reason many people who get DVDs from two regions also get a second DVD drive -- they can play DVDs from one region in one drive, and DVDs from another region in the other drive.
Hope that helps!
