Doesnt it auto do that? if not it got to css, but last i heard it should auto tile it if you enter it once.
I mean, if you insert the background once, it should go like that thruout the entire screen... Ya know what I mean? try it out, if it doesnt work then hey, get rid of it again.. this works mattering on the bg style too a bit i think..
when u make ur templete u gotta make the background thats wat i usally do and it works perfect for me..
What i usally do, is align my temp into the center by using the <center></center> tags and either, if the temp has side bars that can be extended, i use them as a background image, if it looks stupid, just find your <body bgcolor='#00000'>