you need to use a formatter tnat supports fo:float.
http://xmlgraphics.apache.org/fop/compliance.html
For an example, it would be like this:
<fo:float float="right">
<fo:block text-align="center"
border="1pt solid gray"
font="bold italic 9pt Helvetica">
<fo:block>
<fo:external-graphic src="url('smile.gif')"/>
</fo:block>
<fo:block>
Fig. 1: A Smiling Face
</fo:block>
</fo:block>
</fo:float>