Other header-Image on another Site

Hello,

I have the same Header-Image on every Page in my blog. Now I want to set another Image on every Page. On the Half-Life²-Page I want to have this Image, for example.

I tried to paste this code in the pagecode for the page:

<style type="text/css" media="screen">
	#headerimg 	{ margin: 0; margin-top: 0px; height: 200px; width: 800px; }

	#headerimg { background: url('http://marvinimus.ma.funpic.de/mzmapper/wp-content/themes/blacknblue/images/hl/header1.png') no-repeat top;}
</style>

But it doesn’t work.

It changes the code automaticly to this:

<style type="text/css" media="screen"> 	#headerimg 	{ margin: 0; margin-top: 0px; height: 200px; width: 800px; }

#headerimg { background: url(\'http://marvinimus.ma.funpic.de/mzmapper/wp-content/themes/blacknblue/images/hl/header1.png\') no-repeat top;} </style>

How can I solve this problem?

I hope you can help me,

Thanks, Tool

PS.: Soory for the grammar.