I seem to spend a lot of time cutting text from web pages or Visual Studio and pasting it into email messages. Oftentimes this causes all manner of wierdness in Outlook 2003, especially when the email messages are formatted as rich HTML.
I found a nifty utility which will remove most of the formatting information from text in the clipboard so you can paste it as plain text. It's called PureText, it's free, and I find it very useful.
PureText puts an icon in your task tray which you can click to convert whatever is at the top of the clipboard stack into plain text, or you can configure a hotkey to do this and, optionally, paste the text wherever the active cursor sits.