fglrx 8.12.26 can't be compiled against 2.6.18-rc4 kernel (and maybe also some
older). You will most probably get

CC [M]  /lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.o
/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.c:233: error: `UTS_RELEASE' undeclared here (not in a function)
/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.c: In function `firegl_stub_open':
/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.c:505: warning: assignment discards qualifiers from pointer target type
/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.c: In function `__ke_vm_map':
/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.c:3072: error: `VM_SHM' undeclared (first use in this function)
/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.c:3072: error: (Each undeclared identifier is reported only once
/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.c:3072: error: for each function it appears in.)
make[2]: *** [/lib/modules/fglrx.orig/build_mod/2.6.x/firegl_public.o] Error 1
make[1]: *** [_module_/lib/modules/fglrx.orig/build_mod/2.6.x] Error 2
  
Apply this patch against /lib/modules/fglrx and then

	chmod +x build_mod/make.sh make_install.sh
	build_mod/make.sh && ./make_install.sh && modprobe fglrx

						-- JiKos.

diff -ru fglrx.orig/build_mod/firegl_public.c fglrx/build_mod/firegl_public.c
--- fglrx.orig/build_mod/firegl_public.c	2006-06-22 20:30:28.000000000 +0200
+++ fglrx/build_mod/firegl_public.c	2006-08-08 00:59:05.000000000 +0200
@@ -23,6 +23,9 @@
 
 // ============================================================
 #include <linux/version.h>
+/* jikos hack to make this thing compilable against recent kernels */
+#include <linux/utsrelease.h>
+#define VM_SHM 	0x00000000
 #ifdef MODVERSIONS
 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,5,71)
 #include <linux/modversions.h>
diff -ru fglrx.orig/build_mod/make.sh fglrx/build_mod/make.sh
--- fglrx.orig/build_mod/make.sh	2006-06-22 20:30:28.000000000 +0200
+++ fglrx/build_mod/make.sh	2006-08-08 00:48:21.000000000 +0200
@@ -223,7 +223,7 @@
     kernel_release=`cat $src_file | grep UTS_RELEASE | cut -d'"' -f2`
   else
     # UTS-define is in external version-*.h files, i.e. linux-2.2.14-5.0-RedHat does this flaw
-    kernel_release=`cat $linuxincludes/linux/version-*.h | grep UTS_RELEASE | grep \"$OsRelease\" | cut -d'"' -f2`
+    kernel_release=`cat $linuxincludes/linux/utsrelease.h | grep UTS_RELEASE | grep \"$OsRelease\" | cut -d'"' -f2`
   fi
 fi