Or you can Go to the properties of the Zone you want to transfer. If you untick "store the zone in AD" if will great file for you in "c:\windows\system32\dns". Depending on what version of microsoft you are using. It will be in BIND format. So you could easily import this do a unix/linux server.
Just keep in mind that if you do this, AD will not work correct while you do not use active directory integrated mode.
