Hi!

Well, I tried to add this css into my ATO:

body.page-id-345 {
background: url(http://kteis.com/wp-content/uploads/2011/01/shop-background.png) no-repeat scroll center top transparent; margin: 0px auto;
background: #000000;
}

but nothing is showing

Update:

Now they appeared, but only in two (of four) pages.

Your CSS only deals with one page

Yes, I added four different CSS I just put that as an example since all are the same and only page id differs

Update:
Today situation is the same, only two pages show background (I checked in Firefox and Chrome).
And IE shows them all. Weird.

what is the url?

Although IE shows background it also shows some really nasty distortions especially in blog

I will try putting JPG instead of PNG for images, maybe that'll work.
I noticed that when I create PNG buttons they don't show in Firefox and Chrome.

for the landing page (your page 'Blog') you need 'body.blog'. Also this selector 'body.page-id-345,408 {' is invalid - 408 is not a class. Change it to

body.page-id-345,
body.page-id-408 {

Oh, thanks a lot, I found the part of the problem, too.
There were also two backgrounds, I had to change them to background-color and background.