[root@localhost cdrom]# ./VBoxLinuxAdditions.run
Verifying archive integrity... All good.
Uncompressing VirtualBox 1.4.0 Guest Additions for Linux installation...................................................................................................................................
VirtualBox 1.4.0 Guest Additions installation
Unable to insert a test module into your Linux kernel.  This may be because
the kernel was built with a different version of GCC to the one which is
currently installed, or because the kernel header files are incorrectly
installed.  The command 'dmesg' may provide you with more information.
Problems were found which would prevent the Guest Additions from installing.
Please correct these problems and try again.