There's this wicked AWESOME thread
here that has some tips on the costumes, as well as numerous links to help people with any questions they have.
In terms of costumes from ordinary clothes, it depends on what you're trying to do - as in, how much or how little work you want to put into it. I don't have a sewing machine and I have no idea what I'm doing when I mess around with the costumes, but luckily my stuff came out well.
There's also a lot you can do with normal clothes - if you're willing to rip some stuff up [img]smilies/biggrin.gif[/img]