It happens that centos6 may fail to get virtualbox running due to some kind of 'kernel-header' problem, in which the virtual box complains the kernel header does not match. The remidy to this is:

1. yum list gcc kernel-devel. Install these two if it is not.

2. Check the running kernel matches the kernel headers:

uname -r #running kernel
rpm -q kernel-devel # intstalled kernel headers

3. if the two versions do not match, run

yum -y upgrade kernel kernel-devel

reboot.

My virtualbox in CENTOS6 then run successfully after the steps described above.

Reference: http://www.thoughtpolice.co.uk/vmware/howto/centos-5-vmware-tools-install.html