Enable POP in Gmail

In Gmail settings:
1. Click Settings at the top of any Gmail page.
2. Click Forwarding and POP/IMAP.
3. Select Enable POP for all mail or Enable POP for mail that arrives from now on.

In Outlook Express settings:
1. In Incoming mail(POP3): pop.gmail.com
2. In Outgoing mail(SMTP): smtp.gmail.com
3. In Advanced tab,
3.1 Check both "This server requires a secure connection(SSL)" checkbox of SMTP and POP3
3.2 Modify the port number of SMTP to 465, and POP3 to 995

see here and here