OK, I got my ad sense approved recently and i have about 5 website. On my first website, i put 2 ad sense banners ( One horizontal and One Vertical). Using, the Ad Units fucntion. Now, i want to put two more banners horizontal and vertical on another website of mine. - The question is, can i use the previous codes for the first website or do i need to create another banners for this website.

You can use the same code, assuming you want ads of the same size. Recreating new ads would end up giving you that same code. The basic code is the same and by creating a banner just setting some variables like how wide and how high the ad should be and how many links it should show. You're also adding your unique ua string to identify that ad with your account.

The only reason you need to create a new banned is if you want to change any of those things.