Legacy hardware dropped in 5.X

[Henry]

Why was support for some legacy hardware dropped in 5.X? I can't be  
really specific since my knowledge on my old old machine is  
limited... But it installs and works fine on 4.X but can't be  
installed using 5.X.

To try and explain it more, it is an old compaq presario that uses a  
weird AGP? slot to attach another board to the main motherboard. The  
extra attachment board has ISA/PCI slots on it for me to install  
network cards on. This is a problem I see because removing it gets  
5.X installed, but having it attached doesn't.