Very uncommon. In fact, normal e-mail clients just put the message they forward in the body of the mail, so it's just part of the message, not an attachment. Those 'several' people must use a quite strange e-mail program or do something wrong.
To check the validity of what I wrote above, you can do 2 things:
1. Forward a simple message to yourself and see how it looks.
2. Recieve such a strange message not in Outlook, but in another email-program (like Thunderbird) or in webbased environment (like gmail or hotmail, or even the webbased version of your current e-mail provider if it has such).
It's up to you to prove it's an issue with your Outlook and not with the sender of the message.
I am using outlook for my email.I have several people that forward emails to me, but for me to read the original message when I click it it opens a new window and i have click on it and that opens a new window before I can read the message. If it was forwarded three or four times, that's how many new windows it takes. Is that an option I control? I am using XP and office 2000 sr1 220.127.116.1121