Mac OS X 10.8 Mountain Lion is out and ready for download. If you are willing to invest $20 and an hour of your time to upgrade you Mac computer, you won't be sorry.
If you want to make a clean install of the new OS X Mavericks or even the older versions of Mac OS X, than I strongly suggest you to create a bootable OS X key or a drive.
You deleted everything from your USB key or a drive, so there should be enough free space to copy the new files, but you still get the not enough free space message in Mac OS X? This is what you need to do.
VirtualBox is a great free cross-platform virtualization program that enables you to run Windows, Linux, Mac OS X and other operating systems on you Windows, OS X or Linux computer.
If you are more of a visual person and would like to organize your folders and files using different colors, than check it out how to use color labels in Mac OS X.