Well, if you're going from 10.6 to 10.6.4, it will anyway be a combo update. The function of combo update is that it has all the previous updates in it so you can go from e.g. 10.6.1 to 10.6.4. With normal updates, you would have to install 10.6.2 first and then 10.6.3 etcetc... Software Update knows what's the best for your Mac