Using the follow code:

body
{ background: #000000;
background-image: url(Pictures/BritneySpearsWallpaperNo001.jpg);
background-repeat: no-repeat;
background-position: 100% 100%;
background-attachment: fixed;
}

The percentage under background-position doesn't work? Is it the picture I'm using? Is there a way of stretching the picture to fill the page?

Is there a way of stretching the picture to fill the page?
no, there is no way to stretch an image in that way.

position is used to place the image in a specific spot, not change its dimensions.

you will have to use an image editor to change the image to a larger scale and upload the new image to use. smaller resolutions will just see less of the desired image.

and where you positioned it puts it off the page... b/c 100% would be the absolute side of the page.

If ya can't stretch the image then http://www.lissaexplains.com/css.shtml should be edited because it has Percentage in brackets for background-position.

background-position positions the image across the page, it doesn't resize it.

edit: which I now realize is what the other posts in this thread also say :P