Hey Phil,
Not to great with it myself, but from what I know, your stylesheet should load from left to right.
Try finding somewhere in your theme where it says:
<div id="sidebar1"> ~~~~ all the stuff in that sidebar ~~~~ </div>
and moving it after the main part of your page, ie. the content.
I think that might look something like...
<div id="content"> ~~~~~~ </div>
Your second sidebar (on the right) should be right after the content section, so you can grab your first sidebar, and place it before your second sidebar in your index.php file. I may be wrong, but I think that's what you need to do if you want to do that. Like I said, just a suggestion though! :-) Keep up the hard work!