If you have 27 gig not allocated to any partition, then you are away to the races. Boot the install CD ( DVD ) and follow the prompts. You will install the system to the 'free space'. There are tools to partition that space, format it to a linux supported file system, and install the code.
Now, you need to understand some things about booting any system. In order for any OS to load, the BIOS on the system board, will send the hard drive heads to track 0 sector 1 to read the MBR ( Master Boot Record ). Right now you will have a windoze written MBR. During the install of Fedora, or any other linux system, you will be given an option to write a new MBR with a boot manager program. The two most common ones are Lilo, and Grub. You can pick either. Grub is the latest and most flexible one, so pick it. Take the option to write it to the MBR, yes you overwrite the windoze MBR. Grub should get set up to boot either Windoze ( any flavour ) and linux. Leave the defaults of Grub alone for now. On your first boot after the linux installation you will see a screen allowing you to pick windoze or linux. Use the arrow keys to select which you want. You should be able to boot either.
If things go wrong, almost any bug you create can be fixed without loss of the windoze system. Back up your windoze data before you begin.
If you want to know more about grub, search this board, or google it. There is a ton of information on it. It works, and is rock solid. Most problems are created by the user, not the code.
Post back any questions you have. Good luck....