Why?

Your system files are also very important and can sometimes become infected by viruses.  By system files, I could mean just about any files in the Windows directory and its subdirectories, but in particular, I mean all files in C:\.  These include files like:

c:\autoexec.bat
c:\config.sys
c:\command.com
c:\io.sys
c:\msdos.sys

How?

1. In some cases, this procedure can save you from viruses like Chernobyl. You could just restore your system files and possibly be okay. This procedure is much like backing up your registry.  You can back the files up in Windows safely by highlighting them all with your mouse (*not* the folders) and right clicking and choosing copy. 

2. Then go to My Computer-C:-backup (assuming you made the backup directory in HowTo Backup Registry). Once there, right click and choose paste.