Seems as if I'm close
I have added the code to (in theory) make the changes to the correct tables/fields. Here is the code with my changes:
code:
error_reporting(E_ALL);
//Database Info
$dbhost = 'localhost';
$dbuser = 'xxxxx';
$dbpass = 'xxxxx';
$dbname = 'dbname';
// Open database connection
//
$link = mysql_connect($dbhost, $dbuser, $dbpass)
or die("Could not connect");
mysql_select_db($dbname)
or die("Could not select database");
$query = "select username,user_regdate from usersnuke";
$result = mysql_query($query);
while ($row = mysql_fetch_assoc($result))
{
$curruser = $row["username"];
$timestamp = date_str_to_unixtimestamp($row["user_regdate"], TRUE);
$query2="update phpbb_users set user_regdate = '$timestamp' WHERE username = '$curruser'";
$update_result = mysql_query($query2);
echo "Ran update query on user: $curruser with result: $update_result";
}
// test-data
//$date_strings = array(
// 'Nov. 10, 2001', 'Jun 10, 2002', 'Foo 10, 1999', 'x', '', 'Jan 32, 1999', 'Jan 10, badyear', 'jan 31, 1995', 'may 07, 2005'
//);
// perform test and display results
//foreach($date_strings as $date_string) {
// convert to timestamp
//$timestamp = date_str_to_unixtimestamp($date_string, TRUE);
// convert back to string (to make it easier to check result)
//$date_string2 = date('F j, Y', $timestamp);
//echo "'$date_string' => '$timestamp' => '$date_string2'\n";
//}
// Given date string 'MMM DD, YYYY', return unix timestamp.
//
// If date string is invalid:
// If $debug is omitted or FALSE, return 0.
// If $debug is present and TRUE, return 1 if syntax is bad, 2 if month name is bad, 3 if date is bad.
function date_str_to_unixtimestamp($date_string, $debug = FALSE) {
if (!preg_match('/^([a-z]+)\W+(\d+)\W+(\d+)$/i', $date_string, $matches)) {
return $debug ? 1 : 0;
}
$month = month_name_to_num($matches[1]);
if ($month === FALSE) {
return $debug ? 2 : 0;
}
$day = $matches[2];
$year = $matches[3];
if (!checkdate($month, $day, $year)) {
return $debug ? 3 : 0;
}
return mktime(12, 0, 0, $month, $day, $year);
}
// Given month name, return number 1..12.
// Return FALSE if name is not valid.
function month_name_to_num($month_name) {
static $months = array(
'jan' => 1, 'feb' => 2, 'mar' => 3, 'apr' => 4, 'may' => 5, 'jun' => 6,
'jul' => 7, 'aug' => 8, 'sep' => 9, 'oct' => 10, 'nov' => 11, 'dec' => 12
);
$num = @$months[strtolower($month_name)];
return isset($num) ? $num : FALSE;
}
//Close Database connection
//
mysql_close($link);
When I run that I get this:
Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in blah/blah/blah/ on line xxI never said I was a php guru either
Thanks again for all the help!
So if anything I'd like to just fill that field with the existing data, and work on getting it to display from there. 
