altering theme depening on resolution

Hi,

I was wondering how it is possible to switch a theme depending on the resolution of the user. At the moment, my current design is rather… big. But, considering the way it has been designed and my target audience, this is not necessarily a bad thing. However, since there are still people among that group that use a smaller resolution, I was wondering whether there is some way to determine their computer’s resolution and switch the theme depending on that.

Currently, all I wish to do is have them switch between just two themes; the one I am currently using and a theme for everything smaller than X amount of pixels in width. How much work would it be to implement this feature and how would I need to do it (by the way, I dont mind manually imputting the theme names in the php files, instead of doing it through the dashboard)? I should note that I am a graphic designer with only very little knowledge of programming.