Menampilkan Postingan User Tertentu

Gunakan template, archive page lakukan query untuk menarik post dari user A saja.
Bisa dibaca di codex.

http://codex.wordpress.org/Templates
http://codex.wordpress.org/Creating_an_Archive_Index
http://codex.wordpress.org/Function_Reference/query_posts

Ada di halaman codex query_posts bagian parameter
http://codex.wordpress.org/Class_Reference/WP_Query#Parameters

Show Posts for one Author
Display posts by author, using author id:
$query = new WP_Query( 'author=123' );

Display posts by author, using author ‘user_nicename’:
$query = new WP_Query( 'author_name=rami' );

Show Posts From Several Authors
Display posts from several specific authors:
$query = new WP_Query( 'author=2,6,17,38' );