Very good Webinar on sapinsider about HANA. Its a webinar 60 mins which can be request through the site www.sapinsider.com

Title :

Learn How You Will Benefit from a Fully
In-Memory-Enabled SAP NetWeaver BW Powered by SAP HANA

Following is youtube link which explains the BW architecture in very efficient way. The video needs to be appreciated in the way it captured the wholestic view and interaction between various sections in BW throughout version 3.5 , 7.0 .  Awaiting video on 7.3

http://www.youtube.com/watch?v=fovmnSIplpc ( BW 3.5 architecture)

http://www.youtube.com/watch?v=dCcyKmdwVYk (BW 7.0 archetecture)