If you’re still looking for this…
If you want the two sections to be completely separate, you could look into enabling multisite:
http://codex.wordpress.org/Create_A_Network
If you just want a different style sheet and menu in certain sections, you could have different CSS files and custom menus that are conditionally loaded. For example:
if ( is_singular() and is_category( 9, 27 ) ) {
/* Alternate style sheet or custom nav menu */
} else {
/* Default style sheet or custom nav menu */
}