The Xserver can report warning messages to the log file. They can be identified by the (WW) string at the beginning of the line. There are hundreds of possible warning messages and most of them may be ignored, however some may help to explain why things don't work as expected. We try to explain these here.
Your Xserver reports the warning like:
(WW) RADEON: No matching Device section for instance (BusID PCI:1:0:0) found
This means that the driver is able to drive the PCI device (chip) mentioned (here the one with the ID: 1:0:0) but the Xserver cannot find a valid device section for it in the Xserver config file. Without a device section this chip cannot be used. If the config file doesn't contain any other valid device section the server will terminate with the error message: (EE) No devices detected.
Many devices include multiple device IDs on the same slot. Multi-head Radeons, for example, will often show up as both 1:0.0 and 1:0.1. The second device is totally fake, it only exists so the multihead support on certain other OSes will work. You can safely ignore these kinds of warnings.
The X server will check for the presence of APM power management support on startup. If your system does not have APM support, either in the BIOS or in the kernel, or if the device node simply doesn't exist, then you'll get this error message. This is not fatal to server startup, but if you're using APM for power management and you get this message, the server may get confused on power events.