You can't specifically fill a visitors screen. You can only fill the visitors browser window. Not all users run their browsers full screen. At least I don't.
The best way to stretch a background image is to use the CSS 3 property, "background-size: 100%;". However, it doesn't appear that there is wide support for this property yet. The best I can tell is that Firefox 3.6, Opera 9.5, Konqueror 3.5.4, and Safari 3.0 supports some variation of this property but there are also some bugs associated with it. Internet Explorer provides no support.
You can view the source code by using your right mouse button. As you can see from the code, the image is not really defined as a background image. The CSS code uses some positioning and a Z-Index to make it work. I have tested it in Firefox 3.01 and Internet Explorer 7 and it appears to work fine. It is unknown whether it will work in other browsers. IMHO Firefox does a better job of rendering the image. It seems to do a resampling of the image, rather than a simple pixel replication. This doesn't show too much with your image, but if the original image was very small, you would see a big difference.
The only issue that is not covered in the article I linked to is the "DOCTYPE" tag. Your original page does not have a "DOCTYPE" tag, but it is essential to make Internet Explorer work the way we want it to. You will see the "DOCTYPE" tag as the first line of the HTML code. If you are editing your pages on-line you will need to use the Text editor to add that line. Any saving with the Visual Editor will delete this line. It's best if you do all your editing off-line and upload your changes.
Browser: Firefox, Netscape, Sea Monkey, Internet Explorer, .....
Wow Philo, thank you so much for taking the time to type all of that out for me. It has really helped.
When I opened your sample page on IE I could not get the source...but when I opened it in FireFox I was able to view the source info...so thanks again for that.
I will also go look at your website for more hints and tips.... I need to learn how to use all those templates. It seems they are almost all for blogs now, and I already have my blog set up and need other templates. I am still new at all this...and the easiest for me is WYSIWYG...hahahahah
Thanks in advance for the info on templates...will go there soon.