Passing parameters to a NAnt script from CruiseControl.NET is pretty simple. Basically you pass name/value pairs with the -D command line argument in the buildArgs element. Values with spaces need to be wrapped with double quotes. The following CC.NET configuration file illustrates this:

<cruisecontrol>
     <project>
          ...
          <tasks>
               <nant>
                    <executable>C:\Program Files\nant-0.85\bin\NAnt.exe</executable>
                    <baseDirectory>F:\Build\BabelFish2.0\WorkingFolder</baseDirectory>
                    <buildArgs>-D:param1=somevalue -D:param2="some other value"</buildArgs>
                    <nologo>true</nologo>
                    <buildFile>Source/Build/Build.nant</buildFile>
                    <targetList>
                         <target>default</target>
                    </targetList>
                    <buildTimeoutSeconds>2400</buildTimeoutSeconds>
               </nant>
          </tasks>
          ...
     </project>
</cruisecontrol>

The target NAnt script need only reference the properties as follows:

<project name="YadaYadaYada" default="default">
  <target name="default">
    <echo message="Param 1=${param1}, Param 2=${param2}"/>
  </target>
</project>