[TwoD]

The functions seem to be in order, but you are not sending a name to the createCookie function when you call it.
This means you'll check for a cookie named "graffiti_wall", and if it's not there, create a cookie with the name undefined.
Also, I suggest that you include a value for the cookie, even if it's just a 1.

Code:

function createCookie(name,value)
{
	var date = new Date();
	date.setTime(date.getTime()+(30*1000));
	var expires = "; expires="+date.toGMTString();
	document.cookie = name+"="+value+expires+"; path=/";
}
...
createCookie('graffiti_wall',1)