QUOTE(DMAddict @ Jan 3 2008, 11:20 PM)

Pretty sure you're incorrect here StrictPuppet as if you follow the instructions from
here, it will work. Did for me. My dash is now at 2.0.6683.0.
That performs the dash update, which can be performed many different ways, but it does not give you divx playback, which is what the original question was. The only way to obtain the optional media support codec is directly downloading onto your box from the xbox live servers. It will never be available offline, nor is it possible to transfer it from another box, as it is both profile and console "keyed".
I will quote myself from an earlier thread:
QUOTE(StrictPuppet @ Dec 6 2007, 06:58 PM)

The DivX codec is not free for commercial use, therefore microsoft has to pay a licensing fee for each unique device that uses it. The only way to keep track of how many consoles require this codec is to tie it to the individual machine. It make sense from a business standpoint to not embed the codec in the dash update, which is why it prompts you to download the first time you you play a Divx file. If only 40% of consoles use this feature, why would MS want to pay the royalty for every machine out there.
If your console was banned from LIVE you have forfeited the right to obtain services from MS, free to end user codecs included. A pain in the ass, maybe, a logical business move by MS, definitely. This will never be downloadable from xbox.com, in the same way that the ipod support (also licensed by MS for a fee per console) is not available for off console downloads.
Here is a quote from MS regarding the Ipod AAC codec.
QUOTE
The codec you download will be unique to your console, it will not accompany you, for instance, if you move your gamer profile to an Xbox 360 Memory Unit to play at a friend's house.
If you're using a friend's Xbox 360 console, Xbox LIVE Marketplace will allow you to download the AAC codec again. But if you've already downloaded it to your own console, the codec will not work on your friend's, as the codec is only valid the first time it's downloaded by a specific gamer profile.
Expect to see a similar FAQ about DivX as they update their site to reflect the new dash update.