I tried this regular expression

$validate = "^[a-zA-Z0-9'àòèéùì '\.\"\-]+$"
If ($Name != '' && !eregi($validate, $Name)){
$error[] = 'Error invalid character';
}

If I insert this character \ there is no error
why ?

PHP Code:

$validate = "^[a-zA-Z0-9'àòèéùì '\.\"\-]+$"
If ($Name != '' && !eregi($validate, $Name)){
$error[] = 'Error invalid character';
} 


It's nice to put them in [php][ / php] tags.

Try a Preg, it's a bit better.
http://uk.php.net/manual/en/function.preg-match.php

$validate = "^[a-zA-Z0-9'àòèéùì '\.\"\\-]+$"
you dont need to escape dot and minus when they are inside square brackets