Why not use CSS to repeat it then you can shorten it to something like a 50px x 50px square or a 1px by 1000px then just repeat the background left to right, top to bottom or both if it is a pattern, that way the file will only be a few bytes and load with in a millisecond, but still give you the same design.
Do you have an image we can look at?
Also if it is a .png have you compressed it as that tends to cut about 75% of the image weight down, makes it uneditable so make sure you save a back up copy first to make amendments later.
I'm not sure you can, you could split it into 3 as a possible solution due to the fact that the browser would then, well depending on which 1 you are using, download 2 smaller sections of it at once rather than 1 larger 1 all at once. I take it the black bit at the bottom is done via CSS? Because if you give the body at background color of #000 and then lay the background image above the body, you could then reduce the image and save you some bytes.
Could you email me the image?
jazajay at googlemail.com and I'll see if I can get it smaller for you with out splitting it as it would be better overall to keep it as one from a page performance point of view.
Also Is the image full behind the main white section?
You could crop it so only the outline of the image around the white section is there, you would then save a fair few bytes as a result of the reduction that wont be seen 99.9999% of the time. Just an idea but it should load about 3 times quicker if not more.