I know Idle... I should have clarified that statement...
A retrovirus is an RNA virus as opposed to a DNA virus.
The difference between RNA and DNA is that the Thymine in DNA is replaced with Uracil in RNA, because Thymine (and therefore DNA in general) is too large to move through the nuclear membrane.
When a DNA virus uses a cell's nuclear DNA to replicate itself, its DNA cannot escape the nuclear membrane. So, the nucleus fills up with viral DNA and eventually ruptures. In this manner any cell infected with a DNA virus will die.
When a retrovirus (that is, an RNA virus) uses a cell to replicate itself, the replica RNA can pass freely about the cell in a manner that DNA cannot. Consequently, whereas a retrovirus may kill the cell, it is not a foregone conclusion of the replication process the way it is with DNA viruses.
Hence, if you used a DNA virus to try to implant new code into your own genome, it wouldn't work because all of the cells infected with the virus would eventually rupture and die.
A retrovirus might be able to effect a genetic transformation on a multicellular organism, however.
That's what I meant; sorry I wasn't clear.