[CentOS] Multiple Linux instances on the same box - dual/triple/etc boot ?

> I much prefer using the free VMware server for development and
> testing different OS versions.  It's far more difficult to screw
> the pooch using virtual machines, and one can always make snapshots
> before upgrades or major changes making it easy to undo the
> changes and try again.  I find this invaluable when testing major
> software installations.

Yes, this seems like a case where virtualisation is a good solution. 
I've only just started learning to run Xen myself, but the advantages of 
virtualisation over dual/triple booting etc are pretty clear. As well as 
the ones you mention, different machines can also be run concurrently 
and networked.