I have an existing Centos 5 installation. I would like to upgrade to Ubuntu. Thing is, I don't want to be down for as long as it will take to get my entire environment moved over - software installed, connectivity configured, etc. I'd like to take it one step at a time.

But I don't really want to keep rebooting back and forth from the new OS to the old OS. That's what I did last time I upgraded to a new OS, and it got old real fast.

So, since my new MB is virtualization-ready (AMD Phenom II 945 quad-core), I figured I could create a virtual machine, under the new OS installation, that ran the old OS installation.

The problem is that the documentation I've been able to find has been pretty sparse. I've found a lot of possibilities, and little info on which would be capable of doing what I want.

I have a new Ubuntu 9.10 installation, and a second disk containing the Centos 5 installation. And I don't know where to go next.

Any help would be appreciated.