Isn't there an option in Outlook where your email is internet based. That way you can check it anywhere much like with yahoo, etc. You have to set up the account again, I believe. I don't think it's something you can simply change on an existing account. Also, I believe for that you have to click the box to leave a copy on the server.
Hmmm......now I have to go play with Outlook because it's been a while since I set it up that way. Since we have our own mail servers I found it was much easier to just set up the accounts on each machine where they leave a copy on the server for the roaming staff.