When creating something like a Word document (which, of course, could be used as an attachment for an email), you can do what you're trying to do by right-clicking on the link and selecting 'Edit hyperlink'.
However, I've just checked to see whether Outlook Express does the same and it doesn't.
Like Fo3nix, I'd be wary of sending any form of edited hyperlink in an email anyway, because this requires the use of HTML and not everyone has HTML available to them when they receive an email. (That's either because they've got their email client, such as Outlook Express, configured to 'Plain text' or because they use a web-based mail system which only supports plain text).
If you're looking to shorten long URLs, it would be best to use this website to do the job for you:
http://tinyurl.com/
Chris