I think that you are getting a little ahead of yourself on this.
You have several flavors of Linux iso images, I assume from your description, downloaded and possiblly burned to disks. You have some fine distros (flavors) including Ubuntu, which may be a little more user friendly for new users to try first. But let's look at what you have.
Question #1 - First of all, think about what you want to do with Linux. What specific tasks do you expect to do. You are new to Linux and Fedora may or may not be the right choice for you. Your expected tasks will help you decide from the array of fine distros out there. So, what do you want to do, in term of tasks?
Question #2 - why Fedora Core 5 rather than 6, which is newer and may support your hardware better?
Question #3 - what other hardware is in your system, say printers...etc? Do you use a wired cable internet connection, or plan to use wireless?
You have an Athlon 64 system, so, did you download the CD images for an Athlon system? They should have been named something like
FC-5-x86_64-disc1.iso..etc. If you downloaded the i386 images, that will also work, but not optimize your procerssor's power fully.
In terms of partitioning. Did you delete a partition at the end of the hard drive? And you did leave it unpartitioned, correct?
I assume that you got stuck at the partitioning screen? I new installation is what you need to do, but you have to tell Fedora how you want to use the hard drive. See the partitioning page
here.
If this is the case, if you have free space on the drive that you want to have Fedora use, then you would pick
Use free space on selected drives and create default layout. You only mention having one hard drive in your system, so I assume this is the case. If you are installing Fedora on a second hard drive, let us know, as there are some other points to consider before installing Fedora.
I am not trying to discourage you in this process, just have you make informed decisions before you take the plunge. Better to have a plan than try to overcome problems from the start and get frustrated.
The best way to install Fedora, is to read the documentation. You will get a lot of useful information to guide you through the process. See the documentation for Fedora Core 5
here. this should answer a lot of questions that you may have.
Another excellent article is
Fedora Core 5 Linux Installation Notes.