[CentOS] Booting back into CentOS-6

I'm currently running CentOS-7,
but I'd like to re-boot into CentOS-6.5
which I have on another partition.
Although this OS is in the grub list when I boot,
if I try to run it I get a segfault.
I guess this is something to do with the change from grub to grub2?

In any case, I'm wondering if there is any simple way
of booting into both CentOS-6 and CentOS-7?

-- 
Timothy Murphy  
gayleard /at/ eircom.net
School of Mathematics, Trinity College, Dublin