Embedding WebResources: multiple images in folder

[macap.usenet]

Hello,

i am embedding System.Web.UI.WebResources in my C# Class via:
[assembly: System.Web.UI.WebResource("ExtJS.yui-ext.css", "text/css")]

I use this resource with:

Page.Header.Controls.Add(new LiteralControl("<link href='"ExtJS.yui-
ext.css"' rel='stylesheet' type='text/css' />"));

The css file is embedded fine into my website, but it does not detect
the images in my folder 'ExtJS.images'

I am refering to the images in the CSS file like this:

.extjs{background:#fff url(<
%=WebResource("ExtJS.images.default.form.text-bg.gif")%>) repeat-x 0
0;}
But this does not work. What do I do wrong?
Do I have to register the images as WebResources in the same way I
registered the css file ([assembly:
System.Web.UI.WebResource("ExtJS.yui-ext.css", "text/css")]) too?
If yes... where and how?
And another question...
It´s not very clear to my why I have to register the WebResources as
assembly. Does it have any special reason?
Regards,

Martin