I am just trying to get my ducks in order and know when you want to watch certain video files with certain codecs you need to download those codecs from XBL, so far I have only had it ask me once.... are there more that need to be downloaded?

I ask because I am planning to have a modded box not on the network and would like to be as prepared as possible to not have to run a network cable to it in the future if at all possible just to play a certain video file.

After you've got the main update, it will prompt you for one codec update when you try to play the video. For me, it was the MP4 optional support that I had to re-download (as it's changed). Then my divx played.