I've been asked a number of times if there is a good architectural diagram of the processes within BI4 and how they all interact together. In version 3.1 there was a standard slide that SAP released and was well know by everyone, but since version 4 came out, this has been something that has been lacking and most people just put together their own materials displaying the most important parts.
However, I just came across this diagram which is great and shows it quite clearly how it all connects. Have a look and I'm sure you will be the star when presenting this to your clients.
http://help.sap.com/businessobject/product_guides/sbo41/en/sbo41_bip_architecture_en.pdf
There's also this flash version with good information about each server.
BI 4.0 FP3 Platform: View components
Cheers,
Josh