PHP redirection

[Sa177ir]

I am trying to do some redirection within my PHP script, but have been unsuccessful.

I have the following snippet of code - depending on which branch is taken, I would like to redirect to a certain page.  I'm checking the variable hostName to make sure that it contains only alphanumerica characters.  If it has characters other than alphanumeric, redirect the script to page X.  If it's clean, redirect to page Y

$validateString = '^[a-zA-Z0-9._-]+$';
if (!ereg($validateString, $hostName))
{
  //redirect to page X

}
else
{
  //redirect to page Y
}

I have attempted to user headers, but I get the following error:

Warning: Cannot modify header information - headers already sent by (output started at /var/www/apache2-default/coen285/validateLogin.php:8) in /var/www/apache2-default/coen285/validateLogin.php on line 47

Does anyone have any ideas or suggestions to fix the problem?  Any help would be appreciated.

Thanks!

[SharkBait]

Check to make sure anywhere above where you issue the header() function that there is no text being sent to the browser.  No echo's, print() etc.