This is possible with browsers that fully support position:fixed; however you will more than likely want/need to adjust your header and top navigation area so it takes up the same width as your content area. This will give the sidebar the space it needs on the right hand side.
One thing that might be an issue with this is that if someone is using a small monitor or low resolution where part of your sidebar is below the bottom edge of their browser window, they will never be able to see the hidden part of the sidebar. Fixed sidebars work only if the sidebars are short enough to where they do not extend below the bottom edge of the browser window. Things like smart phones and smaller netbooks could have problems.