Hello,
I think for sanity's sake, we should save the data from the hard drive, and do a re-install. That way, you get a good solid chance to see the OS, and learn about it from the ground up.
You would not be able to install linux on the Mac and preserve the files on the desktop. The installation would format that particular partition, and you would lose the files. You could format everything and put YellowDogLinux on the Mac, and that would work, but you will find that OS X has a very nice interface and works so well with what a Mac is meant to be.
YellowDogLinux is a fine product; it is great for older machines that cannot run OS X well (such as this Powerbook G3 333 Mhz that I have here!) but as a Desktop OS, it isn't completely finished as the Mac OS X is.
When you are ready, plan a day to rebuild this machine. Get the data off, and then come see us.

If you want me personally around, I am usually around during the day - central daylight time. I am between jobs.
Christian