If you are trying to install CentOS 4.6 and it hangs on "Probing PCI hardware" then you can fix it with the following workaround.
Before the installer starts, fill in this command:
# linux pci=nommconf
Then you will see the installer works correctly.
Don't forget to edit the kernel after the reinstallation before booting by adding the line "pci=nommconf" to the end of the kernel line.