In order to install this driver, you must copy two files 
"vgaradeon.c" in "/sys/src/9/pc" and "radeon.c" in "/sys/src/cmd/aux/vga".  
After that, you must do the following :

In the directory /sys/src/cmd/aux/vga : in the file "data.c", you must
add the two next lines to ctlrs[] :

--------------------------------------------cut-here----
        &radeon,
        &radeonhwgc,
--------------------------------------------cut-here----

In the file "mkfile", you must add the line to OFILES :

--------------------------------------------cut-here----
        radeon.$O       \
--------------------------------------------cut-here----

In the file "vga.h", ou must add the two next lines :

--------------------------------------------cut-here----
        extern Ctlr radeon;
        extern Ctlr radeonhwgc;
--------------------------------------------cut-here----

In the directory /sys/src/9/pc*
in your kernel config file ("pcdisk" for example) add the next line :

--------------------------------------------cut-here----
        vgaradeon       +cur
--------------------------------------------cut-here----

Finally here are a few lines from my /lib/vgadb :

--------------------------------------------cut-here----
<insert radeon_vgadb>
--------------------------------------------cut-here----

I hope everything will be all right on your config and I wait for any
feedback.  

The driver features some code to take care of the blanking directly
with the hardware. In order to take care of the various blanking modes,
I've used a variable in plan9.ini, which can take the following values :

        *dpms=off
        *dpms=suspend
        *dpms=standby