The interface looks somewhat similar to Vista Media Centre in its basic structure, but with more emphasis on visuals. Also, a new “party” mode will allow an 8 person chat to be carried out regardless of where you are within the Xbox Live community. This party can also move as a group through different games in XBLA and their new Primetime feature, which has multiplayer-oriented party games. The update is expected to come in the fall.

For all you stealthgamers.com visitors, a video showing a method to access the new dashboard. (This hack may not work for all Xbox live users)

Xbox Hack

If you’re somewhat tech-savvy and don’t have problems messing around with code, various Xbox security checks, burning CDs, and things like that, XHavok87′s (name of blog that discovered it) hack might just work for you.
Instead than trying to re-create the instructions here, I’ll just say that the XHavok87 blog entry has them with a high degree of detail. I can’t vouch for the efficacy of the instructions, having not tried them myself.