This will be quick and sweet. Last night someone asked me to turn re-use an old server from having a catalog installed to just hosting primary DNS zones. So before I make this Active directory integrated DNS server to just a primary or do anything worthwhile I wanted to backup the zones. Well how?
First stop the DNS service by doing this command at the cmd prompt “net stop “DNS Server”
Next, just create a separate copy of the “%WinDir%\System32\dns” in my case C:\Windows\System32\dns directory that contains flat files (text files) of your zones. There are also some samples inside this directory, not required to be included.
Lastly is start the DNS service again by doing “net start “DNS Server”
To restore it just stop the DNS service, copy your backup back to the above directory then start the DNS service again and the zones are restored 
METHOD 2
Instructions
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Click the Windows 2008 “Start” button and select “All Programs.” Click “Accessories,” then click “System Tools.” In this list of items, click “Backup Utility.” This is the main utility used to back up important services on your server.
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Click the “Backup” tab at the top of the window. Click the plus sign next to the “Desktop” icon. This expands a list of options. Click “Computer” to expand more options.
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Check the box labeled “System State.” This saves important server services such as the DNS settings and Active Directory users and computer.
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Click the “Browse” button at the bottom of the window and select a location on your hard drive for the backup.
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Click “Start Backup” to save the DNS settings and other administrator configurations on the server. It may take several minutes for the backup process to complete.
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Read more: How to Back Up a Windows DNS Server | eHow.com http://www.ehow.com/how_6869477_back-up-windows-dns-server.html#ixzz1rKrbKOa6
source:
http://technet.microsoft.com/en-us/library/dd392269(WS.10).aspx