Yup. In the general sense of the term "virus" (any malware that can be installed on a computer), there are some kinds of malware, usually called downloaders, which can actually download more malware...
Use a good antivirus to know if you have a virus. Examples are: Avira uit Duitsland avast! uit Tsjechiƫ BitDefender uit Roemeniƫ Computer Associates uit de VS ClamAV - GPL ClamWin - GPL ClamAV voor...
There are a few computer viruses that actually remove other viruses from computers they infect; the most common one is called Netsky (though its creator actually named it Skynet). They were written...