Try making a topic in the Spyware Hell section of the forum, and tell Rorschach (current spyware mod) about the problems you're having. He can probably help you out. And try Hazelnut's instructions, that might allow you to install MBAM.
Also, could you get a screenshot of all the processes in your Task Manager, and post it in this topic? There might be a malware process running that is blocking you from downloading MBAM.