i tried to download via red hat linux official website but i couldnt. i also had tried through red hat linux evaluation process
When you say could not download it, what exactly was the error message? The easiest way to download RHEL 7 or any of the images is to use wget for example:
wget -c -O rhel-7-server-x86_64-disc1.iso "RHEL 7 DOWNLOAD URL provided to you by RHEL portal"
The above will download the iso and store it as rhel-7-server-x86_64-disc1.iso. If from any reason it fails to download entire image simply run the command again from the same directory to continue download.
To install Redhat with MS windows dual boot you need to install windows first, leave some un-partitioned space on your disk and then start RHEL 7 installation.
hope this helps