Factory manuals vs. Bentley manuals

["xudong" <xudong@prisminc.com>]

     I just got my first price shock. Audi will gladly sell me the factory 
     service manual for $375 a set.
     
     Apparently "factory" manuals and "Bentley" manuals are different 
     beasts. But the bentley manual for my 95 A6 is not out yet. (for the 
     pre 92 100 the bentley manual is $160 a set).
     
     So what is the difference between the two?  Which one should I get? 
     (assuming Bentley makes one soon) Is there a place that sells the 
     factory manual for less?
     
     In absense of the above manuals, can some kind soul tell me how to 
     remove the bottom cover that covers the underside of the engine 
     compartment? (92+ 100 or A6). How do I identify the oil drain plug?
     
     I would really like to change the oil in between the 7.5k service 
     interval.
     
     
     Thanks
     
     
     Xudong Yan