Sidebar Shifts to Bottom When Window is Narrowed

This is an old problem I have been dealing with. I like to set my main blog area and the sidebar to relative percentage widths so that people with larger screens don’t have most of the window dominated by the blank areas on both sides. Since the themes I want are usually set widths, I have to go in and change things.

Currently I am using the iNove theme. If I set the main blog post area and the side bar to anything above a total of 97%, then the sidebar slips to the bottom, leaving the right side blank. So I set the main area to 63% and the sidebar to 34%. As it is, if the window narrows to anything below 1050 pixels, the same thing happens.

How can I stop this from happening, even if it means that elements inside the sidebar start sticking outside the borders?

An added benefit would be to get that extra 3% back–it forms a gap in the middle of my blog which is difficult to fill cleanly. Strangely, the gap closes to nothing when the window is narrowed to that 1050-pixel point.

Any suggestions or help would be appreciated!