99.999999% of viruses need admin rights to infect and propagate
Trouble is so does 99.999999% of useful software, particularly if it was written longer ago than last week. After a couple of weeks trying to get MSCV6, VB6, Quicken 2000, PSP7, a DVD burner, ancient scanjet driver, and a few other things (you get the picture) to run on Win2k3 Server without admin rights I finally gave up and gave myself admin rights.