You can install CentOS 5 on another computer or on a virtual machine (vmware). When you finish install you should switch i686 versions of some packages to i586 or i386:
yum list |grep installed |grep i686
In most cases packages that cause troubles are:
To install i586 versions you can do this:
rpm --nodeps -e glibc openssl yum install glibc.i386 openssl.i386 # or download the i386 rpms and install them with rpm
Kernel is a special case because you don't have pre-built i586 kernel.
You can simply extract source from source rpm, copy i686 config and choose Pentium for cpu, and then install. However if you need it again you will have to repeat the steps or copy binary files which is not that simple as installing rpm.
Here is how to build from source (you can use different mirror):
rpm -ivh http://centos.skknet.net/5.2/updates/SRPMS/kernel-2.6.18-92.1.22.el5.src.rpm # this is updated version. you can download the original if you prefer cd /usr/src/redhat/SPECS/ rpmbuild -bp kernel-2.6.spec cd /usr/src/redhat/BUILD/kernel-*/ mv linux-2.6.* /usr/src/linux-2.6.18