Getting the default license key

HI

In Vista Ultimate SP1 64-bit (six edition), how do I get the default
license key (not the activation code) which has been used to install
an edition of Vista SP1 64-bit?

I need this code to insert in the block

Code:

<UserData>
<AcceptEula>true</AcceptEula>
<ProductKey>
<Key>Default license key</Key>
<WillShowUI>Never</WillShowUI>
</ProductKey>
</UserData>
<settings pass="specialize">
<component name="Microsoft-Windows-Security-Licensing-SLC-UX"
processorArchitecture="amd64" publicKeyToken="31bf3856ad364e35"
language="neutral" versionScope="NonSxS" xmlns:wcm="http://
schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://
www.w3.org/2001/XMLSchema-instance">
<SkipAutoActivation>true</SkipAutoActivation>
</component>
</settings>

of a file unattend.xml as key instruction does not allow you to enter
an empty string.

THANKS

BYE