I am currently running Windows XP Pro x86 on:
AMD Athlon64 X2 3800
Gigabyte K8N Pro-SLI
Gigabyte 7900GT 256 MB
1 GB Corsair TWINX Memory
250 GB Seagate SATA
40 GB Seagate IDE (removable)

I have Windows installed on the SATA drive and want to install fedora core 5 on the removable drive. I have the ISO's for Fedora and would like to know what I have to do to be able to dual boot. Also, is it possible to boot from the removable drive automatically when it's connected and from windows when the removable drive is removed?

To answer the question simply, no. At least not "automatically."

In order to boot from any drive in your system, the bios must be set to boot from that drive. This means going into your bios setup and changing the boot order of the drives.

See the related thread below entitled Trying to install FC5 on an USB HD to dual boot from a laptop with WinXP.

In order for an OS to boot, automatically, it needs to be set in a bootloader on the MBR of the boot drive, as set in the bios, or you need some sort of boot disk (floppy or CD based) that allows Linux to boot.

Of course, you can also set the USB to boot first, then if the drive is not found in the bios, have the second boot device be the sata drive. However, you bios needs to support this function.

Also, as noted in the related thread, Fedora does not load the modules (drivers) for a USB boot (at least not in the previous versions) to boot off of a USB drive. Doing so requires some good knowledge of Linux and changing the initrd file in Fedora to do so properly.

Fedora and other Linux flavors are designed to allow a dual boot on a system's internel hard drive.

Is there any reason why you don't want to do this?