Installation virtualbox 4.2 sous centos 5.6

The VirtualBox Linux kernel driver (vboxdrv) is either not loaded or there is a permission problem with /dev/vboxdrv. Please reinstall the kernel module by executing    

'/etc/init.d/vboxdrv setup'    

as root. If it is available in your distribution, you should install the DKMS package first. This package keeps track of Linux kernel changes and recompiles the vboxdrv kernel module if necessary.   

/etc/init.d/vboxdrv setup

Stopping VirtualBox kernel modules                         [  OK  ]
Uninstalling old VirtualBox DKMS kernel modules            [  OK  ]
Trying to register the VirtualBox kernel modules using DKMSError! echo    
Your kernel headers for kernel 2.6.18-308.24.1.el5xen cannot be found at    
/lib/modules/2.6.18-308.24.1.el5xen/build or /lib/modules/2.6.18-308.24.1.el5xen/source.    
                                                           [ÉCHOUÉ]
  (Failed, trying without DKMS)
Recompiling VirtualBox kernel modules                      [ÉCHOUÉ]
  (Look at /var/log/vbox-install.log to find out what went wrong)