You can download the iso files for Windows 10 tech preview from here: http://windows.microsoft.com/en-us/windows/preview-iso. I would recommed installing to a virtual machine or another hard drive since it is a beta and it might have problems in day to day use. You can download virtual box from here: https://www.virtualbox.org/wiki/Downloads. You should have atleast 8GB RAM for the VM install and enough harddrive space (you need to create a virtual harddrive which is a file on your hd). And you shouldn't need Windows 8 to participate in that program afaik.