Depending on teh distro you choose (I'm really only familiar with Red Hat/Fedora's anaconda installer), the installer should ask you about partitioning (you can probably also choose to let the installer auto-partition your drive), so it pretty much amounts to the same thing.
Anaconda, at least, is smart enough to know you have a Windows partition and can install on any free space you have on the drive, or wipe it out entirely if that is your wish.
Keep in mind that
ShadowAce uses Fedora. It is a bit less 'user friendly' to new Linux users. i run OpenSUSE, which is a bit more user friendly, but have heard good things about the ease of use of Ubuntu (and it's other derivatives with different desktop environments) and Linux Mint.
This system has been Microsoft free for five years now, and i don't miss it.
Software is installed through the use of Software Repositories.
The major difference between Linux and what you are familiar with is that Linux is a true multi-user system. Unlike Windows, one does not log in as an Administrator for normal use.