Hi jankent, Welcome to Dell Community. I will answer your question briefly. Let us know if you have more questions.  If you are referring to Dell's "factory restore", a factory restore will remove the infection, depending on if the factory image is still accessible. In addition, it is going to depend on what type of infection you have (specific rootkit) as to whether the image can be accessed via the MBR. It’s unlikely but not unheard of for the recovery image to become corrupt or infected. 
Will the restore PC by Symantec on my Dell Dimension 5000 PC running Windows XP remove the rootkit on my PC?
removing rootkit