Believe it or not, I had the same problem .. I had modified the DOCTYPE tag in the default.aspx file for a different reason and didn't notice the change, all of my settings pages ( admin skin ) would display all the controls centered.
I changed the DOCTYPE back and now the control display normally ( left-justified )
look at the default.aspx file in the root of your DotNetNuke folder and make sure the DOCTYPE tag looks like this...
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">