Modified to enable html letters.

class.user.php
Looks for a <html> tag in the body of the message. If it exists it adds the content type html.
around Line 83.

Added this blip.
Works on wordpress 3.01 at least.

$header = 'From: "' . $replacements['/%sitename%/'] . '" <noreply@' . str_replace('http://', '', $replacements['/%siteurl%/']) ."\n";
if(strstr($msg,'<html>')) {
$header .= 'Content-Type: text/HTML; charset=ISO-8859-1' ."\n";
$header .= 'Content-Transfer-Encoding: 8bit'. "\n\n";
}