So Im using css to make my page layout. Ive sliced all the images and got them lined up, etc. The only problem is I need more space for my content. Im afraid that if I do it incorrectly it will load the content background pics sepratly as they were all different pics. Id like for it to load the pic only once and then just display the same pic over.... is that clear as mud? What would be the best way to extend it? Could I just copy and paste all the content code over and over again like this?

#content {
height: 350px;
width: 678px;
background: url (url);
#content {
height: 350px;
width: 678px;
background: url (url);
#content {
height: 350px;
width: 678px;
background: url (url);

Or......just double the height of my content so that it will display the pic twice. which would be faster and better?

I don't think it is quite as clear as mud, but your CSS above certainly won't work.
You might want to try:

			 				#content { 
 height: 350px;
 width: 678px;
 background: url (url);
background-repeat:repeat-y;
}

Which will just tile it downwards as far as necessary (and it won't load the image multiple times either).

Thanks

and perhaps you know how I could get my layout centered?

Give the main container a width.
In CSS, set this: margin: 0 auto;
In CSS, for older versions of IE on the body set this: text-align: center;