Okay so, it's easy, but you need these two:
PowerShell 2:
http://support.microsoft.com/kb/968930/en-gbDnsShell (DNS Management Module for PowerShell):
http://code.msdn.microsoft.com/dnsshell/The first will be pre-installed if you have 2008 R2, otherwise you will need to upgrade PowerShell 1 to PowerShell 2 (PS 1 is pre-installed on 2008).
DnsShell is my management module, once you have it all you need do is this in the PowerShell prompt:
Import-Module DnsShell
$OldServer = "YourOldDnsServer"
$NewServer = "YourNewDnsServer"
Get-DnsZone -ZoneType Forwarder -Server $OldServer | New-DnsZone -Server $NewServer
If you want to test it on one use:
Get-DnsZone whateverzone -Type Forwarder | New-DnsZone -Server $NewServer
And please let me know if you have any questions about any of this.
HTH
Chris