Well ya Ubuntu is Linux. As well as Fedora, Suse, Gentoo...and 100's others. They are just different flavors of Linux. Think of it as XP home and XP professional. Or the 4 (are they 4?) flavors of Vista....
As for your apps, some apps would work on Linux (Firefox, VLC Player and other stuff), while other apps would have a substitute that would replace your current one, and probably do the job better anyways

. And if both fails you could either emulate (Cedega and/or Wine) or use virtualization. Plus, you would probably find other apps that you wouldn't find on Windows, that would make your life so much easier