Hiya Lisa - yours does display ok for me in IE8 & FF - *eventually* - but at 435kb it is quite a heavy file to have loading on each page as a background image. If I optimise it via photoshop I can reduce the file size to 15kb without noticeable loss in quality.
Also, if you are repeating on an x axis, it doesn't need to be 1024px by 800px - it could just as easily be 20px by 800px, this would leave a file size of around 4kb at optimum quality. That's over a hundred times smaller - it would load so much faster.
It may be that the large filesize of the image may be (partly?) responsible. Slower machines would take an age to load the pages!
You could try using the attached image to see if the file size is the issue.