I'm sorry, I don't have Office 2003 nor IE7 nor those misbehaving mails, so I can't replicate your problem. All I can suggest: change the text size in IE (it's in the View-menu in IE6) and see if that makes a difference).
If you can't find it, try the Computer Help forum.
I recently upgraded to IE 7 and since then some of my e-mails print from office 2003 extremely small so it's hard to read them. I have checked my printer settings and all seem ok. It doesn't happen on all e-mails, only one's that have an original message and a reply, and even then not all of them. Any ideas how I can get the messages to print normally?