You need to swap the float left to float right and visa versa in the CSS...like this...
FROM THIS...
.loginbox.twocolumns .loginpanel {float:left;width:49.5%;border-right: 1px solid;margin-bottom:-2000px;padding-bottom:2000px;}
.loginbox.twocolumns .signuppanel {float:right;width:50%;margin-bottom:-2000px;padding-bottom:2000px;}
TO THIS...
.loginbox.twocolumns .loginpanel {float:right;width:49.5%;border-right: 1px solid;margin-bottom:-2000px;padding-bottom:2000px;}
.loginbox.twocolumns .signuppanel {float:left;width:50%;margin-bottom:-2000px;padding-bottom:2000px;}
Just add this last corrected lot of CSS to the end of your CSS file in your theme. core.css file if it exists.
You will also need to Purge all cache too. This last thing is important otherwise you will not see your changes.
Should do the trick.
Mary