Instaup2date – Finding direct url for Software Updates

Hello, Sorry if I'm repeating a question, I was unable to find anything while performing a search. I want to update my catalog file for 10.6. I'm trying figure out how to find the direct download url's for software updates. I notice that some updates in the 10.6.2 Vanilla catalog go to either http://support.apple.com/downloads/DL9* and some go to http://appldnld.apple.com.edgesuite.net/* For instance, how can i find the correct url for Safari 4.0.5 Snow Leopard to place in my catalog file? Thanks for your help, ken