Fixing Windows: Your operating system is installed 1st on your new computer and it directs traffic (data activity) between your software programs, your hardware and your input.  Sometimes it becomes corrupted over time and needs to be re-installed or maybe cleaned off and freshly installed again. 

Windows ME: This is an installed option if you are buying a new computer now.  I upgraded from 98 Second Edition to stay current.  I like the new bells and whistles but have spent hours combing the net looking for something to speed it up. Here is a WinMag article about ways to do this.

Windows 98: Most of us are using 98.  Best features are the drop and drag start and programs menu that make desktop shortcuts easy.  I don't really find it either faster or more stable.  I do find it necessary if I want to run the latest browsers and other software programs. 

Windows 95: Those of you who have stayed with 95 to avoid hardware upgrades are probably running the fastest operating system of all right now.  The programmers seem to assume that each upgrade will automatically be run on the top of the line latest machine.  In doing so they are forcing people into new computers.  If I thought programmers really cared about the end uses or even sales of their products I might suspect a conspiracy.