Hi Erek,
Why would you have line breaks to position an image? Just use something along these lines;
#body {
background: url(my image url) center center fixed;
/*Other possible values include: top,right,bottom and left*/
}
That's the biggest issue with using lage images as backgrounds, use a photo editing application to find out what format and output quality sorts your purpose best.
As for your last question, if you just like that portion of the image showing, crop it accordingly and position it where you like it to be displayed.
All the best,