Cheers :)

4 - Post title - this is really hard to see, but the post title and the breadcrumbs right below it are not aligned, even though I changed the padding on both to 0px. There's actually a 1px difference between them, and I don't know why!

That *is* hard to see, or at least I'm not seeing it. Hmm. The only things I can think of are either that you're counting the 1px border currently around the posts or you're seeing a natural small space around some font letters. You can see where the font truly stops if you add an underline temporarily for illustration purposes and preview:

.entry-title {
	text-decoration: underline;
}

3 - How can I center the items in the menu?

Looks like you got this one covered by using the following CSS:

#menu-primary div {
	margin:0 auto;
	width:480px;
}

Nice work!

2 - I want the header image to be centered. Originally it WAS centered, but when I "fixed" the .header so that it wouldn't move when I scroll, the header image alignment changed from center to left.

I checked and it's centered right now, but not fixed. Looks like you removed your fix? If you'd still like help on this one, would you mind creating a new help request for it and pasting in the CSS you used to try to fix the header element so I can see what you did before? Unless the requests are all really closely related, i.e. all text color change questions or all very simple, then I think it's nicer to have them in separate requests. It gets messy when there are multiple numbered items in one thread that each maybe need back and forth replies.

1 - I want to move the search widget in the header down so that it's under the header image, in line with the menu.

For this, I would just recommend putting it in the right bucket on the Appearance → Widgets page in your blog dashboard.

I started a second blog and bought the CSS upgrade. I've been playing around with it for a few days but on certain issues I've reached the point where I'm stumped. Starting from the top of the page:

In the header:

1 - I want to move the search widget in the header down so that it's under the header image, in line with the menu.

2 - I want the header image to be centered. Originally it WAS centered, but when I "fixed" the .header so that it wouldn't move when I scroll, the header image alignment changed from center to left.

3 - How can I center the items in the menu?

4 - Post title - this is really hard to see, but the post title and the breadcrumbs right below it are not aligned, even though I changed the padding on both to 0px. There's actually a 1px difference between them, and I don't know why!

Answers to any or all of these questions will be greatly appreciated. Thanks!