Hi
Try first to clean temp catalog, Start - Run - %temp% and remove the files. If they are in use reboot first.
The problem is most likely that something tampered with one or more of these files:
Config.nt Autoexec.nt Command.com
From DOS paste following lines one by one:
%CDROM%:\i386\config.nt_ c:\windows\system32\config.nt
%CDROM%r:\i386\autoexec.nt_ c:\windows\system32\autoexec.nt
%CDROM%:\i386\command.co_ c:\windows\system32\command.com
At %CDROM% you have to write the path to your CD were you put XP CD.
Reboot and retry, this is a "common" error and not related to certain SW.
Good luck