Since you mention Word 2003 documents in your post, I'm going to assume you
are using Outlook 2003. Here are some of the things you should check.
1) Set message format to plain text or HTML (See Tools > Options > Mail
Format tab)
2) Make sure Outlook isn't configured to covert to Rich Text (See Tools >
Options > Mail Format tab > Internet Options button. Dropdown in the middle
of the dialog should be set to convert to HTML)
3) If the person(s) you are sending to are coming from your contacts folder,
then go to the contact record in question and open it. Double click on the
email address. Make sure it is set to let Outlook decide.
4) You may have to disable Word 2003 as your e-mail editor (See Tools >
Options > Mail Format tab)