Upgrade installs are the standard fare for most people going out to a retail store to purchase an Operating system. Which Operating systems are supported upgrades? There are a few slight differences between the two OS's that will play as a factor in your decision. First off let's see about Home Edition.

WindowsXP Home Edition "Upgrade" Path's supported

    * Windows 98
    * Windows 98se
    * Windows ME

Professional is a little more robust in this department, understandably..

Windows XP Professional "Upgrade" Path's supported

    * Windows98
    * Windows98se
    * WindowsME
    * WindowsNT4 Workstation
    * Windows 2000 Professional
    * WindowsXP Home Edition

You will notice 95, NT3.51, and any Server versions are *not* supported as upgrade installs. To be honest, if your box is running 95, you'd probably want to skip XP on a system that old anyway. Same for an NT3.51 box. And upgrading a Server OS with a Workstation or Consumer class OS doesn't make sense, so these restrictions aren't a big deal. Besides, the "Server" edition of XP (.NET) won't be available till next year.

Let's wrap this thing up, shall we?