I´ve been working in a solution for this case in OpenErp:
<document>
<template>
<pageTemplate>
<stylesheet>
...
<paraStyle name="main_footer" fontSize="7.0" leading="7" alignment="LEFT" spaceBefore="0.0" spaceAfter="0.0"/>
...
</stylesheet>
...
...
<!-- Page Footer -->
<place x="1.5cm" y="0cm" height="1cm" width="19.0cm">
<para style="main_footer">[[ o.name or '']] | Página: <pageNumber/> de </para>
</place>
<drawString x="4.9cm" y="0.74cm"><pageCount/></drawString>
...
Basically, it "draws" the <pageCount>
tag at the left of my footer text. The solution from @alartur is more elegant but it does´t work in the OpenErp rmltopdf converter.
We must use Helvetica font at 7px for our footer text because is the default font used in the rmltopdf code for <pageCount>