Hmm... you could forward all of your sent mail to your POP3 account by setting up a filter that forwards everything 'From:' your Gmail address, or you could just set up the POP settings so that you can use Thunderbird or whatever to access you're Gmail account.
Also, if you don't have a POP3 account, and really just want to access the sent mail, you could set up a second Gmail account, forward all of your sent mail to that one, and then access that one with your email client.