I think I can safely assume that you're either new to Vice City or new to the multiplayer version of this game. Well, since this is not a lag-less game, simply aiming straight and shooting at a person will not kill him/her, unless your target isn't moving at all. You have to, thus, lead your shots, or in other words, aim your shots ahead of where you think the person will be moving towards, in order to beat the lag. This is especially the case for long range shots with weapons such as the m60. Some people may lag more than others, and you just have to simply decide how much you want to "lead" when you're shooting.
Hope this helps.
TLK.akiharu
Hope this helps.
TLK.akiharu