[calorie]

1) Go to vB ACP -> Plugin System -> Add New Plugin:

Product: vBulletin
Hook Location: global_start
Title: news_index active
Plugin PHP Code: code is below
Plugin is Active: Yes

if (THIS_SCRIPT == 'news_index' AND !$vbulletin->options['bbactive'])
{
	// either turn board on or set custom message
	$vbulletin->options['bbactive'] = 1;
	// $vbulletin->options['bbclosedreason'] = 'msg';
}

2) Go to vB ACP -> Styles & Templates -> Replacement Variable Manager -> Add New Replacement Variable:

Style: your choice
Search for Text: images/smilies/
Replace with Text: http://www.domain.com/forum/images/smilies/

Tip: also check out the vB online manual