I can only speak for Red Hat since version 7, but there is not much to explain to get everything up and running...
Just insert the setup cd and reboot your system. All you have to do is follow the onscreen instructions. It will automaticly install a boot loader and configure everything to run your old OS (it will call it 'DOS' by default, but you can change it of course). You should read the help texts on the left hand side and you should be fine. You will have to choose between two bootloaders - i would recommend Grub, it is definitely easier to configure and looks cooler, too
...but if you really cannot get your head around one of the options to choose, you can come back here and ask about it - but have no fear, it is easier than you might think!