Changing Layout to Relative Width

I’m trying to adjust my blog (HUMS) so that it is flexible. I’m trying to adjust the style sheet so that the body is done by percentages rather than pixels but I’m stuck. When I introduced the body wrapper to get side borders, it threw everything out of whack. Trying to get sidebar next to the body without any luck. Tried introducing percentages into the style sheet but it only adjusted the width of the sidebar/entries (so that it was thinner) rather than fitting the content to the page. Can anyone help point me in the right direction?