I don't think in your HDD of just 80 GB, much space would be left after installing Win 7. Still if you want to install Fedora on it, you need a separate partition to install it. I would recommend a partition of 10 GB at least.
- First backup your data. Just to be safe.
- Then pop in the Fedora install disk. And select the option "Free Space" when prompted.
(If it asks to select partition select the partition where to install Fedora. Be careful not to select any other drive which may be of the same space. I can be confusing since in Linux partitions don't work like in windows. (No C:, D: but Sda1, Sda2). You will have to guess the partition after watching the size of the disk.)
- After selecting the drive, just proceed and rest of the setup should be finished with almost no user interference.
- After Fedora gets install, you will get the select OS option whenever you will boot your PC (called GRUB).
- Enjoy.
And it's always better to follow a good guide like this:
How to dual-boot Fedora 14 and Windows 7
