I love wordpress so much. WordPress 2.9 support Post Thumbnail.

add following code in function.php of theme. You will see Post Thumbnail in right sidebar. You can add Post Thumbnail.

add_theme_support( ‘post-thumbnails’ );

see more in there

http://justintadlock.com/archives/2009/11/16/everything-you-need-to-know-about-wordpress-2-9s-post-image-feature