general html help via tumblr

I’m trying to customize one of their free "theme’s" and am having trouble with this inline CSS stuff.

I’ve figured out a couple problems, but I’ve got just a few to go I think.

my page, using "the minimalist" theme:

I can’t figure out how to center images (or any other thing that’ll pop up in the future) since I changed the width to 800px instead of 600 or whatever default was.

I also want to be away with the entire header (from the ask, archive, etc.. links up to the top and replace it with an image+image map to integrate into the site (i’m still waiting for all the domain stuff to get figured out so it’ll have a cohesive domain…experience?).

I’m gonna use to make the image map after I make it in (i don’t pirate and often go without the cool toys).

thanks for any help you can offer!