My concern is only to make Desktop dual bootable where Winodws 7 is already installed and I want also install RedHat 5 Linux. I want to know what settings in BIOS are required to be changed or what is the proper procedures to do so.
You shouldn't have to make any changes to your BIOS.
When you install your distro, it should detect the other OS and offer to modify the bootloader.
Question: Are you installing Red Hat on a separate drive or just a partition on the same drive?
Either way, the bootloader will be changed on the drive / partition that you presently have Windows 7 on. When you boot, the bootloader will present you with an option to boot Windows or Red Hat. I am not sure which bootloader Red Hat 5 will be using. The popular ones are LILO and Grub.
Another question: Red Hat 5? Either I'm imagining it or I think that was the first distro of Linux I played with back in the late 90's. Red Hat moved their free for download desktop OS to Fedora, they have reserved the name Red Hat for their enterprise paid for product.
I cut my Linux teeth on Red Hat based distro's, they use RPM's (Red Hat Package Management) for installing software. Later on I moved to Ubuntu which is a Debian variant that uses dpkg (Debian Packages). I found the Debian package management to be more robust and intelligent when it comes to determining dependencies. Through work I have used Debian and Mandrake. All good distro's, but I really like Ubuntu.