Did you try to insert the DVD (or an install USB stick) and boot? And then try to install?
Why you would need a Windows to install openSUSE is beyond my understanding. I do admit that on the systems I install there often is some Windows relict, but I always overwrite that as if there was none.
Just follow the instruction linked to on the down load page. I think you are thinking about secure boot and you can turn that off or if you really want leave it on openSUSE will be OK either way.
That is the way I understand the question, as well.
The latest news on that issue is that the motherboard manufacturer’s have included a method for turning that security step off or on.
But, as gogalthorp says, openSUSE has been designed to install both ways. You can install it with Secure Boot UEFI (the “signing” problem you have been reading and worrying about) either turned on, or turned off.
Wouldn’t everything in your current system be connected to the new motherboard and fire up without needing to install anything? Always worked for me when upgrading my motherboard, CPU and RAM.
When did operating systems start getting installed on the motherboard?