Bernicc, please look at the error message you posted. Apparently the kernel sources for your currently running kernel are missing but the details are mentioned in the file /var/log/vbox-install.log. See also the user manual section 2.3. After you installed the missing package do /etc/init.d/vboxdrv setup to perform the recompilation of the kernel modules.
And no, we cannot add the kernel sources to the dependencies of the RPM package because there are many kernel packages with different names available.
