I heard somewhere that by removing a virus' DNA or RNA and replacing it with new DNA, viruses or rather their shells, can be used to cure various genetic disorders such as cancer. I do not know much about virus shells (obviously), so if anyone has some good info, it would be much appreciated~

it's proteins and lipopolysaccharides in the protein coat that constitute antigens when introduced into a host and stimulate the host immune system, like macrophages, to use phagocytosis to engulf and destroy the virus by identifying its antigens as foreign.

I think you are referring to "Gene Therapy", where the vector (carrier) of genetic material into cells can be a virus:

In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene. A carrier molecule called a vector must be used to deliver the therapeutic gene to the patient's target cells. Currently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists have tried to take advantage of this capability and manipulate the virus genome to remove disease-causing genes and insert therapeutic genes. ( http://www.ornl.gov/sci/techresources/Huma...netherapy.shtml )

Also see http://www-micro.msb.le.ac.uk/3035/peel/peel1.html where there is a section on the application of gene therapy for cancer treatment ( http://www-micro.msb.le.ac.uk/3035/peel/peel8.html ).

It's very early days with gene therapy, but the prospects are amazing, helped in a major way of course by outcomes of the Human Genone Project.