How do you make a background repeat y ...?

Hi.

I'm trying to repeat a "background" through my site. Must be in the middle exactly and with 100% height.

Here is the url:

http://www.i-bestseller.com/index1.html/

I have tried the background-position tag, but it seems to only move the background to the right and doesn't seem to affect the top and down.

Can anyone give me some advises?

Does anyone have any ideas for how I can achieve the best look for my index page?

I do very much appreciate anyone help!

Thanks...