But have you any idea what might be preventing a horizontal scroll bar from appearing?

The overflow property set to hidden for the #page element is causing that. A rule like that is usually added to clear floats. It wouldn't be good advice to remove without researching the theme a bit more because presumably the rule was added by the theme author for a good reason, and it could break the layout in unexpected ways.

For the moment I'm considering whether to shift everything by around 75 pixels towards the left, thus (I believe) making it fit even the smaller 1024 pixel screens.

So, is it possible to have a search function on the "feed-wrap" type of page at all?

directly under the bar of navigation menus, on the right-hand side

Not very reasonable: you've got a dropdown there.

As regards the total width of my configuration, I was trying to keep it so that it would fit all standard computer screens (albeit with maximum browser widths); I didn't realize that it went beyond those that are 1024 pixels wide. I could eliminate a bit of space on the left-hand margin, moving the columns a bit towards that side, and then it should fit even those screens.

What in the CSS coding could be preventing a horizontal scroll bar from appearing?

1024px wide monitors: 14.6%
1280px wide monitors: 10.5%
1366px wide monitors: 23.6%

What you have to do is to put the search widget into the sidebar and then use the specific widget ID for that search widget and use position: absolute to move that widget over and to the right of your content. This is just example code and after putting the search widget into the sidebar, you will have to look at the source code on your site, find it, and get the ID for that particular widget.

#search-4 {
position:absolute;
left: 1200px;
top: 100px;
}

You will have to adjust the left and top values as needed. I've specified "left" instead of right because your site is pinned to the left border of the browser window.

Frage an die Entwickler: ist es nicht doch möglich, die Suchfunktion auf Überschriften und Tags, vielleicht Autoren auszuweiten?
Ich weiß, dass das Thema schon mehrfach behandelt wurde, hab aber noch keine befriedigende Antwort gefunden.

Der Blog bei dem ich Hilfe benötige heißt altdinklage.wordpress.com.

#header {
	padding-bottom: 0
}

Nice work!

Any idea how to do this using CSS? I've searched the forums high and low, but cannot find anything.

Many thanks - the blog is: http://robinlennoxstewart.com

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!

#access {
background:#333;
display:block;
float:left;
margin:0 auto;
width:100%;
position:fixed;
bottom:0;
left:0;
z-index:50;
}

#access .menu-header,div.menu {
margin-left:10px;
}

Initially where it says margin-left I had auto, but I changed it yesterday to try to limit the menu overlapping with the search bar.

I use twenty ten on one of my blogs and would love a fixed menu at the bottom but don't want it to be my menu from the top so guess I will do it another way. Did you use your menu and fix it there or a widget? I might have to poke around in your code unless you want to share?