Where to find AGP details

Good morning all,

I am trying to understand a little about how the AGP works.  How are the 
AGP memory addresses determined?  0x0f0000000 is for a fujitsu, 
0xE8000000 seems to work on my ATI with Josh Grams's 2005 source. Can 
anyone please point me to a datasheet or article that explains AGP 
configuration, or is this more a BIOS set-up thing?  It appears that ATI 
don't give away any technical info.  I've found 
http://download.intel.com/design/chipsets/datashts/25302704.pdf but this 
doesn't shed much light (may be I have to spend more time on that though?)

Thanks,
Jason