Windows XP does include Outlook Express.
In Outlook, all you have to do is set up a mail account in exactly the same way you did it in Outlook Express.
You enter your email address and your username and password for the POP mail server, and this is where a lot of people go wrong. The way the mail account dialogue is configured can confuse you into thinking that you have to enter the username and password that you use to login to your ISP - and that's not necessarily the case. What you must do is enter your MAILBOX login details, and if you have your own domain name for instance these will be different to your ISP login.
The other thing that sometimes catches people out is the increasing tendency for ISPs to require a login to the SMTP server, so make sure that if yours does need this information you enter it under the advanced settings tab - with an ISP mailbox the login will be the same as for the POP3 inbound mailserver.
Double-check all that and see how it goes.