Problem Number One is not having a password, and that's a killer. Your IT Guy wouldn't be able to give you your password (they're encrypted), but he could at least reset it for you. That problem pretty well trumps the other concerns.

"Outlook Express" is a mail client living on your five desktops, while "Outlook" is Microsoft's email server. You may or may not be using Outlook server; it's kind of expensive, especially compared to all the no-charge open-source software out there. Your server is more likely to be something like Postfix.

Do you recall ever using a Web interface to email? It's common to install it alongside an email server, and if it exists and you used it in the past, your web browser might remember the login credentials. Most webmail packages let you change the password, and if you get in using a stored password, change the password to something you know first thing. Webmail is usually installed at the same address as the email server, as a web site ending in something like "/mail/" or "/webmail/" or "/squirrelmail/".

You can access your email from any computer that can connect to the mail server, as long as you have a mail client and the login credentials. The other computer might have Outlook Express installed, or you could download an open-source email client like Mozilla Thunderbird (the open-source incarnation of the old Eudora commercial email program). BTW, your "username" on most mail systems is your email account, so you have half of what you need. What's left is the password, and if you're the type to reuse the same password in multiple places, you might have a shot at guessing it. Connect the mail client to the email server address using POP3 (the one protocol all email servers support) on port 110 to retrieve mail and port 25 to send. Most mail servers are configured to require authorization, so check that. Then start to hack the password.

You might get lucky, but your expectations should be low. This is one big Hail Mary pass. Good luck.