I hope this is the right place to post, 

I have just finished building a new web page in html 5 and using a jquery slider effect to horizontally scroll across the web pages. 

Now I need to design a background at 8000x1000px so it all "flows and connects" prefectly between each seperate background image

So I need to divide this large 8000px into 4 x2000px to install as 4 seperate background files. 

The problem is I cannot for the life of me work out how to do this with illustrator (currently using cs3), i can create a file at 800px but cannot work out how to divide into 4 seperate images pixel perfect.

Any help would be greatly appreciated. 

Thanks
Kristian