Blockyness on my computer?

Hi, for a while now... I have not known what it is, but I play a game called World of Warcraft. And I am on a desktop computer, its a 07-08 I believe, so its fairly new... When I am playing, I notice that my game play is very blocky, blocky meaning... when my character moves, he will like... skip when he moves, in a slow rate. This is very annoying and I would like to get rid of it, can anyone please give me some ways on how to decrease the blockyness on my computer? If you all think that it is lag, it