If you just put in the cd and let it do the "default installation" then it will probably overwrite everything.
My advice (just another noob's advice) dont go for command line installation, go for GUI. its a lot easier.
also before you install linux, make sure you have one "ext (2 or 3)" partition ready and some amount of swap space also!
after you free up this space then the installation cd will autodetect and install linux there keeping your windows and your data safe.
hope this helps you! c ya!!