help please

[khaleejy]

hi

i have notice that about 05% of new members type their email like that: www.ex@hotmail.com
i dont know why they write www. before their email.. maybe cuase they think it works like a website or something like that. anway i need to do something like that:

if (www. isin $email) {
$email = str_replace("www.", " ", $email);
}

i dont know where/what/how should i moditfy.. database? register.php? register template?
i dontknow aranoid:
please help me.. and type the code to me if you can

thanks