[CentOS] where is ProxyHTMLURLMap for C5 ?

Hello,
I'm setting up a reverse proxy in Apache (httpd-2.2.3-11.el5_1.centos.3)

I have some pages being served which contain hard-coded names of machines
behind the proxy, which obviously do not resolve on the client side.

I found an Apache config item called ProxyHTMLURLMap* which supposedly
will allow me to re-write these hostnames, but can't seem to find the
apache module to install

     Starting httpd: 'ProxyHTMLURLMap', perhaps misspelled or defined
     by a module not included in the server configuration

Anyone know what the name of that rpm/module is for Centos 5?
Thanks!