<adminhtml_catalog_product_edit>
    <PRODUCT_ATTRIBUTE_SET_ID_9>
    <reference name="product_tabs">
        <action method="addTab">
            <name>my_custom_edittab</name>
            <block>customtabs/adminhtml_catalog_product_edittab</block>
        </action>
    </reference>
    </PRODUCT_ATTRIBUTE_SET_ID_9>
</adminhtml_catalog_product_edit>

<adminhtml_catalog_product_new>
    <PRODUCT_ATTRIBUTE_SET_ID_9>
    <reference name="product_tabs">
        <action method="addTab">
            <name>my_custom_tab</name>
            <block>customtabs/adminhtml_catalog_product_tab</block>
        </action>
    </reference>
    </PRODUCT_ATTRIBUTE_SET_ID_9>
</adminhtml_catalog_product_new>