When asked what exactly does 'clean' mean when you describe a computer that is 'free from foreign software'? To me, this would be a system that has just been built so you are dealing with a hard drive that will be partitioned and formatted at the time the operating system is installed. After this, an antivirus program should be installed, followed by completion of all operating system updates. Next, Java should be installed, followed by a basic 'adobe acrobat reader' which will give the computer .pdf file compatibility which has become standard on the Internet. A handful of anti-spyware and malware programs should then be installed. At time of this writing, which you can always check the OPTIMIZING tip followed by a visit to the SOFTWARE/SUPPORT page for all that are in this list. Currently I would suggest CCLEANER, SPYWARE BLASTER, SPYBOT SEARCH & DESTROY, AVG ANTISPYWARE AND AD-AWARE. I would also have these as shortcuts on your desktop in the order mentioned as this is what I would then run on a daily basis (the optimizing tip explains this in greater detail).
If your system has a DVD Burner, then it should have also come with packaged burner software which should be installed as all operating system before VISTA will not burn to DVD directly through windows. Only direct cd burning can be done prior to VISTA.
This would be a clean system. Other things that can and probably should be done for preventative maintenance and backup is to purchase drive image software such as Acronis True Image or Norton Ghost and create a backup image partition which can then be used as routine backups are made using this software.