I would think Ubuntu would be a better choice for an older computer but not in lieu of Mac OS. The advantage is that you could build on your knowledge of Linux and open source OS's and that may lead to finding other free solutions that don't break whenever the new commercial release of Snow Leopard which has proven to be buggy. I that that as far as functionality goes Mac OS is going to out perform Ubuntu on photo, video, web and most multimedia solutions.
I'm sure there are good open source options for your functions but if you have any professional media application needs stick with Mac OS. As the other poster mentioned you could run both on the mac, you can also demo ubuntu without fully installing it. I think you would be crazy to mess up your brand new iMac at least at first with any thing other than the goodness of Mac.
Then you can mess it up later. I'm jealous you have an iMac.
Ubuntu has the ability to boot from a live cd. Download the . Iso from ubuntu.Com and burn the disc.
Place the disc in your cd-rom drive and restart your computer. Select cd as boot device and give the operating system a try. If you like it, install it on your hard drive.
It is a very capable operating system and can be a great choice depending on what you need to do with your computer.
.I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.