Blog HTML help needed, please

Okay, I've been playing around with my layout, colors, title background, etc. But what I now want to do is a wee bit more complicated. I want to add my own background (http://img530.imageshack.us/img530/6012/daisybkgsmts9.jpg) to my blog. I've tried a few things, over and over, but am having no luck.

This is one of the things I found online and have been trying to do:
body {background-image: url(URL address of your image);

However, I am not having any luck with this. Can anyone out there help? Or refer me to someone who might be able to help me?

Much appreciation for any advice,
Jill Marie

PS~ If you happen to know the correct size (pixels width and height) for backgrounds, I'd appreciate that information too. :)