From the SwingInterop build file in the 2.2b16 examples directory:

    <!-- try and find JavaFX SDK -->
    <target name="find-javafx" unless="javafx.sdk">
        <property environment="env" />
        <condition property="javafx.sdk"
                    value="${env.ProgramFiles(x86)}/Oracle/JavaFX 2.1 SDK/"
                    else="${env.ProgramFiles}/Oracle/JavaFX 2.1 SDK/">
            <and>
                <contains string="${os.arch}" substring="x86"/>
                <available file="${env.ProgramFiles(x86)}/Oracle/JavaFX 2.1 SDK/rt/lib/jfxrt.jar"/>
            </and>
        </condition>
    </target>
    
    <!-- check if jfxrt.jar exists in specified JavaFX SDK directory -->
    <target name="check-javafx">
        <available file="${javafx.sdk}/rt/lib/jfxrt.jar" property="found-javafx"/>
    </target>

    <target name="javafx-missing" unless="found-javafx">
        <fail>.
            Ant could not find JavaFX 2.1 SDK. Please set [javafx.sdk] on command line:
            eg. ant -Djavafx.sdk="C:\Program Files\Oracle\JavaFX 2.1 SDK"
             or ant -Djavafx.sdk="C:\Program Files (x86)\Oracle\JavaFX 2.1 SDK"
        </fail>
    </target>

Perhaps the logic should be, look for JavaFX in the Oracle directory for JDK6 on windows, but otherwise look for JavaFX relative to the jdk location.