See this Adium thread for an example. No idea how it's done in Drupal, but one solution would be to auto-detect plain-text URLs, replace them with an HTML link to the site, and if the link text exceeds a particular length, to truncate it.
43 Folders is powered by Drupal, which rules. The site was designed and made wonderful by the astounding Chris Glass. Ben Durbin is the sine qua non and our personal consigliere. 43f’s web hosting is sponsored by A2.