best repair manual and reset tool

Ok, still a newbe - what is the best repair maintenance manual to get and where do I go to get the reset tool for oil changes? And how much of a job is it to replace the serpentine belt on the 3l engine? The car came with NO maintenance records and the oil looks quite dark.
Sailorman
2001 Z3 Coupe

The Bently manual is the one to get.
I have the oil reset tool from ebay, it was $40.
You can get the one with the code reader here.
http://www.bavauto.com/shop.asp#undefined