Hey… Have you used any @media queries? Everything seems so sqeezed together at <600px….
you should add max-width: 100% to your logo image.
you should also set .homerightcolumn and .int_leftcolumn both to width: 100%; clear: both; on @media (max-width:600px)
And i think that should solve your problem. Feel free to check some of the videos made by Chris (owner of css-tricks) related to responsive webdesign. It should give you more insight on responsive webdesign and/or troubleshooting it. You can also try a framework like Bootstrap or Foundation for responsive webdesign or at least a CSS responsive grid system like Gridify for a more faster/simpler way to code responsive design.