I can answer at least part of your question.
C1 C2 C3 .... Chipset/PCI bridge | | | | +---+----+ .... -----+
C1, C2, C3 etc are the white PCI connectors.
This is where you plug in a PCI card.
These are often called PCI slots
The line at the bottom is the PCI bus.
All devices on the same PCI bus can directly communicate with eachother.
Since they are on a shared bus, only one device can be active at the same time.
The part I marked Chipset/PCI bridge is often where the PCI bus is connected to other parts of the computer. This can be a connection to the chipset, or another PCI bus.
I found some link on Ars Technica's archives which might help:
http://archive.arstechnica.com/paedia/p/pci-express/m-pcie-1.html
http://archive.arstechnica.com/paedia/p/pci-express/m-pcie-2.html
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