This dell issue is a real pain in the *rse. I installed an old copy of Wordperfect on my father's new with XP Pro Dell because he wanted it, and it overwrote some XP system files. The OS popped up a dialog box pointing out that a system file had been overwritten with an older version and to inert the OS CD so it could re-set it to the latest version, and this dialog box just kept popping up in front of all other windows.
But of course you have no CD. Only way out was a full re-install of the OS from the hard disk, and all applications from scratch.
I don't understand why Dell have done this, unless it is for cost.
BW