Some programs will accept students from related disciplines into their graduate physics programs. Usually electrical engineering, maybe aerospace engineering, maybe mechanical engineering or applied mathematics are also considered.
Architecture is interesting. In my experience, the architecture majors were some of the hardest working graduates I ever met in graduate school. You may be able to convince using your application, that your background coursework makes you an acceptable candidate. I figure it is likely that in your architecture program, you probably needed courses in calculus, and some introductory physics, and maybe classical mechanics and possibly some engineering courses. Good grades in these courses would bolster your argument.
I read what Vanadium had to say about the physics GRE / qualifying exam. I do not think it is quite this troublesome. Of course, the better score the better, but I would put a lower limit of 60-65 % rather than 75%, on the GRE, depending on the University you are applying to.
I think a score lower than 50% would not do much good.
Now when I started, my GPA was low (but improving), and I had a part time job. I needed letters of recommendation, and coursework to enhance my graduate school application. I went to a course professor and offered to take his course for credit, and the university allowed be to be enrolled as a "special student". Now mind you, I was not financially supported by the school, and I was not enrolled as a Master's student, and I had to pay the tuition out of my own bank account, but it was the beginning of my graduate career. I was accepted with funding at another graduate school the next year.
In light of this, I would say your chance of being enrolled in coursework (as I was), might be quite good, Being instantly enrolled in a masters program, might be harder, but might be doable.
