Centering an Oversized header

Hello,

I’m using a slightly hacked version of the Default wordpress theme and I have a larger image than the standard size. How do I get my header image centered on the page instead of just lined up with the main column? I would very much appreciate some guidance. I’ve been trying to do it myself for a while with no luck so far.

Also if I could ask, where do I find the code for the little verticle borders on my main column? I’d like to remove them.

I’m grateful for any help you can give me. Here’s the site I’m working on: http://johnleszczynski.com/.

Thanks!!