I need to know what exactly is an ERP system and why is it important/useful. 
Where did it come from? 
Why do companies use it/need it? 
What are the functions and features of an ERP system? Please go into detail on
those functions / features.
Basically I need a detailed explanation to a beginner what an ERP system
is. One page of links is not what I am looking for. So please
go into some good detail.

I also then need information on Activities-Based Costing systems and ERP.
How is an ERP system important when setting up and using an
Activities-Based costing system and why would a company want to do
that?
What types of things are done in an ERP system to set up ABC or get it going? 

If you need a specific ERP system to compare and answer the questions
to, then please use BaaN. I don?t need any explanation about what is
an ABC system (activitites-based costing), I at least know that much :)

Thanks and please remember to put the sources of where you got the
material. I will tip well if I get a lot of good and usefull material.