Ubuntu comes in multiple flavors. The standard Ubuntu uses the Gnome desktop. Kubuntu uses KDE as it's desktop. Xubuntu uses XFCE as it's desktop.
Then there's Edubuntu. It comes with lots of educational software for children. Gobuntu is a flavor of Ubuntu that comes with only free software, no proprietary drivers like nVidia or proprietary programs like Flash.
There's Mythbuntu that turns your PC into a media center, Ubuntu Mobile is designed for touch screen PCS. And the newest is Ubuntu Netbook, designed for sub-notebooks like the EeePC.
If you're going to be doing a lot of video and audio work I recommend the Ubuntu flavor designed for that.
All software packaged for Ubuntu (the filename will end in .deb) will run on most any flavor of Ubuntu. Just use Synaptic (Gnome) or Adept (KDE) to choose the software you want and it will download and install it.
The different flavors are therefore not that different. They will all run the same software. The primary difference is in how they are initially set up.
With tens of thousands of different software packages available, each Ubuntu flavor has to choose which ones to install during your initial setup. For instance, the standard Ubuntu might have OpenOffice installed and few games, while Edubuntu will have lots of educational packages and some games and little productivity software.
But since you are free to crank up the package manager and install anything you want they really aren't that different.
Gaaaack! 1.1 gig for studio.. Sheesh.