You do need to give Linux it's own partition. Preferably a few. As far as where the partition is physically located on the drive it doesn't matter. Some people will argue that it does but it does not. Distro's like Slack, Gentoo which make YOU config EVERYTHING, yes you'll prob wan't to do it the way they tell you. But if Windows was installed first any Distro with a good installer will see that and config for it accordingly.
BTW: What are you planning to run?
To answer your added question, NO you cannot install on the Windows Partition (If thats what your asking).