http://www.bdegan.com/2004/09/gmail-for-mail_08.html
here you go
🙂
On the other hand, gMail changed its service today and you can setup a forwarding address in your gmail account, so you don't need this hack anymore
🙂
Although I don't know if your ISP will allow sending emails through their SMTP server with an @gmail.com email address.
have fnu!
Palad1