If you plan to run CentOS 5, why not install it directly? If you want a smaller installation medium, you can download the os/<arch>/images/boot.iso ISO image and do a minimal netinstall. You could also use just the first CentOS 5 CD and do a minimal install (disable all software groups).
Cool, thanks. Just grabbed one of the DVDs from here
http://isoredirect.centos.org/centos/5/isos/i386/
and did a minimal install in just a few minutes.