I need some clarification to the question.
If the question is 'Can I have two copies of the Atahualpa Theme in my blog?' the answer is yes, name the folder a different name. I have 'Atahualpa332' and Ataqhualpa333' both in my 'Themes' folder, but I can only use one at a time.
If the question is, 'Can I have two Instances of WordPress running in the same mySQL database?', the answer is yes, but you have to have two seperate databases.
If the question is, 'Can I have view one blog with two themes at the same time?' this has been asked many times on the Wordpress support forums and the answer seems to be not without a lot of hacking.
It would be cool though