Simple Template Tutorial
First off open a new document about 800 by 600 pixels with a white background.
Now with the rectangle marquee tool, choosing a 'fixed size' of 600 by 400 pixels, on a new layer fill the selection with white.

Now with this new white rectangle layer selected and the background layer, align the white box into the middle.

Now with only the white box layer selected, using the rulers with snap turned on (view -> snap), position rulers on each side of the box.

This means now when you use the rounded rectangle shape tool, with a radius of 20px, you can make sure its in the center of your image, and a nice round size - by clicking nearer the guides it snaps to it, so draw this new shape around the guides.

How you can hide the guides if you want (ctrl+h), as its time to add the following blending options to this shape:

The blue colour is hexadecimal "3CCDFF".

Now with the Horizontal Type tool, you want to type your sites name at the top.
I use Century Gothic, the same blue as above, 60pt, sharp, with the first bit in bold.

Now add the following blending options to the text:


You can now position the header where you want. I used the alignment tool to get it center.
Now the main box is done, along with the header, its time for the navigation.
Drag a guide down to below the header text, and then with a fixed rectangular marquee size of 600 by 40 pixels, on a new layer fill the selection in with blue like below:

After deselecting the selection, add the following gradient overlay in the blending options:

Now you simple add the text you want for your links. I seperate mine with "|"'s for effect, and find 18pt about right, with other settings the same as with the header.
After the navigation text has been aligned with the navbar, you should have something like this:

The finished layout, complete with code, can be downloaded here.
Please let me know via the contact form if there are any gleaming errors.