The function is called isValidURL and is displayed in it's simple glory below :)

<code lang="PHP">
<?php 

function isValidURL($URL)
{
	return ereg("^((http|https|ftp)://)?(((www\.)?[^ ]+\.[com|org|net|edu|gov|us])|([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+))([^ ]+)?$", $URL);
}

?>
</code>

Here is some examples you can run to test the function. 

<code lang="PHP">
<?php 

$url = array();

$url[0] = "www.pinellascounty.org/park/01_Anderson.htm";
$url[1] = "http://www.440WestCondominiums.com"; 
$url[2] = "https://136.174.187.14/bcc/reef/treasure_island_reef.htm";
$url[3] = "www.ci.gulfport.fl.us/history.htm";
$url[4] = "www.ci.gulfport.fl.us/City_Departments/Leisure_Services/Casino/Casino.htm";
$url[5] = "umUxiKeZOfP1BHL6fYEZnXEqaNvC7ijpJ1cr94ENZTDZZMV4iZRKwV0LgjLcIsH";
$url[6] = "ftp://rspdesign.net/";
 

foreach ($url as $k => $v)
{
 
	if(isValidURL($v))
	{
		echo "URL is question: " . $v . "<br />";
		echo "URL is <span style=\"font-weight: bold; color: blue; \">valid!</span><br /><br />";
	}
	else
	{
		echo "URL is question: " . $v . "<br />";
		echo "URL is <span style=\"font-weight: bold; color: red; \">invalid!</span><br /><br />";
	}

}
 
?>

</code>