Looks fine in Firefox but not in IE or Safari

Did NetRivet do your original site?
They (or whom ever did) should upgrade you to the current version and deliver a site that will validate, here http://validator.w3.org/ which is the link samboll gave you.

Why I won’t shoot wedding photos – I don’t know how.
If you are completely new at this, don’t learn by messing up your commercial site. Set-up another directory, like hmmm, practiceblog, install the default WP and learn there.

Errors.
Your site has quite a few but remember they are cascading, so very often when you correct one, many will go away. This doesn’t mean you should try to correct them if you are just guessing.

Hope there aren’t duplicates of this post, but they’re getting swallowed up.

last try

Try this: replace the following

<center><div id="header">
		<img src="http://danieldunnphotography.com/wp-content/themes/prophoto/images/header-logo.jpg" style="display:none;" alt="" />
		<h1 id="blog-title"><a href="http://danieldunnphotography.com/" title="Daniel Dunn Photography" rel="home"></a><span></span>Daniel Dunn Photography</h1>

with

<div id="header">
		<img src="http://danieldunnphotography.com/wp-content/themes/prophoto/images/header-logo.jpg" style="display:none;" alt="" />
<h1 id="blog-title"><a href="http://danieldunnphotography.com/" title="Daniel Dunn Photography" rel="home">Daniel Dunn Photography</a></h1>

Then remove the </center> a little further down the page

In your stylesheet create

body {text-align:center;}

Find div#header
I’m not sure why you’re floating the h1#blog-title to the left (rather than text-align:left) but mine is not to reason why.
Make sure that for the div#header in the stylesheet there is an overflow:auto which prevents all contained elements flying off all over the place (breaking out of their box)

Yes, as kmessinger mentions, you have multiple errors and the first thing to do is to fix them

What you need to do is get the html validator plugin for firefox, which will show you all your mistakes when you view source.

If you’re doing this yourself, then you’re doing fine – it’s a learning curve, and boy! does it eat into your time.

But it’s the only way if you want it to look exactly how you want it (unless you’re very rich, in which case it’s not the only way – but you then have to spend a lot of time finding someone reliable who’s going to be around long-term etc.)

The usual reason for not showing up in nasty old IE is the wrong doctype – put a strict doctype declaration at the top of the page, and then you can’t go wrong provided you then go through the page removing all errors. You only need one error for it to cascade down, as mentioned above.

Strict xhtml usually simply has /> added at the end of it and isn’t in any way difficult e.g

<img src="blah.jpg" />
<div> another blah </div>
<h1> more blah </h1>

For example, one missing end div e.g no </div> will usually destroy the whole page as the browser tries to figure out what the heck is going on.

Buy html, xhrml and css by Elizabeth Castro, which is the most useful book I’ve ever found on html. I use it all the time and I’ve been learning this stuff for years.