Upgrading from XP to Vista or Vista to Windows 7, do we have to have the first operating system installed first. I wonder if we can install the upgraded system with the upgraded software by only somehow prove that we do have the first software, such as temporarily inserting the CD of the first software into the drive for verification during the installation of the second. If it is possible then we would have a clean install even though we are doing an upgrade. Though we still can install the upgraded system straight after the first I suppose it would take longer time and some residue of the first system would still somehow remain.
Of course, we can only do upgrade in this way if we can afford to wipe out the drive or partition.
