1.E' sufficiente utilizzare due volte la funzione mail(), una per l'email all'utente, una per la tua:
Codice PHP:
function SendEmail(){ 
         include(
"header.php"); 
         global 
$db$prefix$email$username$site_name$site_email$site_url
          
         
nav_menu(); 
          
         echo 
"<form method=\"POST\" action=\"users.php\"> 
               <table align=\"center\" border=\"0\" width=\"500\" cellpadding=\"2\"> 
        <tr> 
            <td colspan=\"2\" align=\"center\">Spedisci email a (
$username)</td> 
        </tr> 
        <tr> 
            <td width=\"100\">To:</td> 
            <td><input type=\"text\" name=\"email\" size=\"27\" value=\"
$email\"></td> 
            </tr> 
            <tr> 
            <td>Oggetto:</td> 
            <td><input type=\"text\" name=\"subject\" size=\"27\" value=\"\"></td> 
        </tr> 
        <tr> 
            <td valign=\"top\">Messaggio:</td> 
            <td>Salve 
$username,
 
                            <textarea rows=\"20\" name=\"msg\" cols=\"80\">Testoooo 
</textarea> 
                            
 
                            --------------------- 
                            
 
                            
$site_name
 
                            
$site_url 
                             
                        </td> 
        </tr> 
        <tr> 
            <td></td> 
            <td><input type=\"hidden\" name=\"action\" value=\"do_SendEmail\"> 
                            <input type=\"submit\" value=\"INVIA\"></td> 
        </tr> 
     </table>"

          
         include(
"footer.php"); 

function 
do_SendEmail(){ 
         global 
$email$username$subject$msg$site_name$site_email$site_url

         
$message "Salve $username,\n\n"
         
$message .= "$msg\n\n\n\n"
         
$message .= "-----------------------\n"
         
$message .= "$site_name\n"
         
$message .= "$site_url\n"
          
         
$to $email;
         
$header "From: $site_name <$site_email>\n"
         
$header .= "Reply-To: $site_email\n\n"
         
$mailallutente mail($to$subject$message$header);
         
$to "mio indirizzo"
         
$mailame mail($to$subject$message$header);
         if(
$mailallutente&&$mailame)){ 

                
msg_redirect("".LOGIN." ".EFFETTUATO." ".CON." ".SUCCESSO."","users.php","5"); 

         }else{ 
               echo 
"<h3>" 
                    
."<font color=\"#FF0000\">An error occurred while sending the email.

                    
."</font>You can try:

                    
."1- Check the email is correct.

                    
."2- Call your hosting provider to allow the function mail(); to send E-mails.

                    
."3- If your running the script on localhost (on your pc) you have to:

                    
."a: edit php.ini file. Click on (Start) menu then chose (Run) type in (php.ini) and hit Enter.

                    
."b: Look for: 

                    
."------------------

                    
."[mail function]

                    
."; For Win32 only.

                    
."SMTP = localhost

                    
."-------------------

                    
."replace with:

                    
."-------------------

                    
."[mail function]

                    
."; For Win32 only.

                    
."SMTP = mail.palnet.com

                    
."SMTP_PORT = 25

                    
."-------------------

                    
."you can change mail.palnet.com to any local email provide. we just need there mail server"
         } 


2.temo che non che dipenda dalla codifica della mail, comunque, a mio parere, la cosa migliore è utilizzare una mail in html, che può contenere qualsiasi carattere speciale. Per fare ciò, è sufficiente specificarlo negli header della mail:

Codice PHP:
function SendEmail(){ 
         include(
"header.php"); 
         global 
$db$prefix$email$username$site_name$site_email$site_url
          
         
nav_menu(); 
          
         echo 
"<form method=\"POST\" action=\"users.php\"> 
               <table align=\"center\" border=\"0\" width=\"500\" cellpadding=\"2\"> 
        <tr> 
            <td colspan=\"2\" align=\"center\">Spedisci email a (
$username)</td> 
        </tr> 
        <tr> 
            <td width=\"100\">To:</td> 
            <td><input type=\"text\" name=\"email\" size=\"27\" value=\"
$email\"></td> 
            </tr> 
            <tr> 
            <td>Oggetto:</td> 
            <td><input type=\"text\" name=\"subject\" size=\"27\" value=\"\"></td> 
        </tr> 
        <tr> 
            <td valign=\"top\">Messaggio:</td> 
            <td>Salve 
$username,
 
                            <textarea rows=\"20\" name=\"msg\" cols=\"80\">Testoooo 
</textarea> 
                            
 
                            --------------------- 
                            
 
                            
$site_name
 
                            
$site_url 
                             
                        </td> 
        </tr> 
        <tr> 
            <td></td> 
            <td><input type=\"hidden\" name=\"action\" value=\"do_SendEmail\"> 
                            <input type=\"submit\" value=\"INVIA\"></td> 
        </tr> 
     </table>"

          
         include(
"footer.php"); 

function 
do_SendEmail(){ 
         global 
$email$username$subject$msg$site_name$site_email$site_url

         
$message "Salve $username,\n\n"
         
$message .= "$msg\n\n\n\n"
         
$message .= "-----------------------\n"
         
$message .= "$site_name\n"
         
$message .= "$site_url\n"
          
         
$to $email;
         
$header "From: $site_name <$site_email>\r\n"
         
$header .= "Reply-To: $site_email\r\n";
         
$header .= 'Content-type: text/html; charset=iso-8859-1' "\r\n";
         
$mailallutente mail($to$subject$message$header);
         
$to "mio indirizzo"
         
$mailame mail($to$subject$message$header);
         if(
$mailallutente&&$mailame)){ 

                
msg_redirect("".LOGIN." ".EFFETTUATO." ".CON." ".SUCCESSO."","users.php","5"); 

         }else{ 
               echo 
"<h3>" 
                    
."<font color=\"#FF0000\">An error occurred while sending the email.

                    
."</font>You can try:

                    
."1- Check the email is correct.

                    
."2- Call your hosting provider to allow the function mail(); to send E-mails.

                    
."3- If your running the script on localhost (on your pc) you have to:

                    
."a: edit php.ini file. Click on (Start) menu then chose (Run) type in (php.ini) and hit Enter.

                    
."b: Look for: 

                    
."------------------

                    
."[mail function]

                    
."; For Win32 only.

                    
."SMTP = localhost

                    
."-------------------

                    
."replace with:

                    
."-------------------

                    
."[mail function]

                    
."; For Win32 only.

                    
."SMTP = mail.palnet.com

                    
."SMTP_PORT = 25

                    
."-------------------

                    
."you can change mail.palnet.com to any local email provide. we just need there mail server"
         } 


Spero di esserti stato utile!