For those stuck with obsolete computers for which you are unable to find functional operating systems, you may find this useful. Although a laptop is used as an example here, it equally applies to obsolete desktops.
http://www.desktoplinux.com/articles/AT6185716632.html

Just one thing, many of the images that you download are in .iso format and have to be burned to CDROM. Now, you are probably thinking, what the heck is an .iso image and how do I burn it to a CDROM. Here is a free CD burning program called DeepBurner to simplify the process. Of course you will need access to another computer with a cdburner in order to install and use it.
http://www.deepburner.com/