Placing a horizontal tabbox in a vertical tabbox is not possible in ZK7.
The only workaround i have is to make the outer tabbox also horizontal.
Please check this issue.

<tabbox id="tabOut" orient="vertical">
<tabs width="24px">
<tab label="A"/>
<tab label="B"/>
</tabs>
<tabpanels>
<tabpanel>

<tabbox id="tabIn" orient="horizontal">
<tabs width="24px">
<tab label="AA"/>
<tab label="BB"/>
</tabs>
<tabpanels>
<tabpanel>

</tabpanel>
<tabpanel>This is panel B</tabpanel>
<tabpanel>This is panel C</tabpanel>
</tabpanels>
</tabbox>

</tabpanel>
<tabpanel>This is panel B</tabpanel>
</tabpanels>
</tabbox>