[souperman]

You can get the user avatarrevision and locate the file if it's stored on the hdd.

$avatar = "http://www.domain.com/customavatars/thumbs/avatar".$vbulletin->userinfo['userid']."_".$vbulletin->userinfo['avatarrevision'].".gif";

That's just the gist, here how I would do it:
Check if the user has an avatarid
If user has avatarid, then get the fileurl of the avatar from the avatar table
if user doesn't have an avatarid (avatarid = 0), then check if user has an avatarrevision > 0
if avatarrevision > 0 then you can get the url path from my code above using the userid and avatarrevision
if avatarrevision == 0 and avatarid ==0, then user has no avatar and display the no avatar url

Hope my pseudo code helps you out.

--------------- Added [DATE]1336002405[/DATE] at [TIME]1336002405[/TIME] ---------------

Here's what I use in one of my external scripts:

function get_avatar_url($avatarid)
{
	if ($avatarid == 0) 
	{
		$sql = "SELECT user.avatarrevision 
				FROM user  
				JOIN customavatar 
					ON user.userid = customavatar.userid 
				WHERE user.userid = '".mysql_real_escape_string($user_id)."'
				LIMIT 1";
		$result = mysql_query($sql);
		
		if (mysql_num_rows($result) > 0) 
		{
			$data = mysql_fetch_array($result);
			return "http://www.domain.com/customavatars/thumbs/avatar".$user_id."_".$data['avatarrevision'].".gif";
		}
		else 
		{
			return "http://www.domain.com/images/noavatarmini.gif";
		}
	}
	else 
	{
		return "http://www.domain.com/images/avatars/thumbs/".$avatarid.".gif";
	}
}

In my case, the avartarid is the given. To make it fit your purpose I would do a LEFT join on the customavatar table to get the avatarid and any other useful info.

I would recommend to do the join on the query that's already getting your user information to save resources. If you post your query I can help you out with that.