A clean install is when you would have it turned on for the first time. There is nothing else there but windows stuff.
If you want to 'refresh' your windows files, consider re-formatting
It depends on what it is. If the files from the program are still on your computer, you can go to Windows Explorer and look for the "setup" of the program.
Yes, it is possible. When you run the setup program, setup will ask you whether to install a fresh copy or to repair the existing copy of Windows.
The XP setup program is a 32 bit program, while the 2000 setup program is a 16 bit program.
No. You can install a new version of Windows by running its setup program from within Windows itself, or by booting from the installation media (CD/DVD/USB drive).
The autorun.inf file is not crucial to the installation process; it only brings up the setup program automatically when you insert the disk. You can still perform an upgrade by running the setup program manually, or perform a clean install by booting from the CD. Note that a Windows XP disc missing this file is highly unusual, and if this file is missing, it is quite likely other contents may missing, damaged, or have been tampered with.
You should probably choose Windows Setup because that is the program used to install windows. If you were not to upgrade anything you would probably notice that Windows Setup is not there. (but its also a matter of opinion)
What methods are available for booting into the Windows Setup program on a stand alone PC
You cannot install Windows ME over Windows XP from within XP. If you must (for whatever reason) install Windows ME, you will need to boot from the CD.
It's not possible to "take too long." The setup program will simply wait for any needed input.
Unattended
Insert your Windows 98 CD and reboot your computer. Begin the Windows 98 setup process. It will tell you that it does not recognize the filesystem on the hard drive, and will ask you to reformat it. Do so. It will then format the hard drive and reboot the computer. Start the setup program again, and follow the on-screen prompts to install Windows 98.
It is a program that you run off your Mac; it helps you prepare, setup, and install windows. It has simple easy to follow instructions and makes the task of installing windows on your Mac easier.