BillyS - 1:08 am on Nov 15, 2007 (gmt 0) From Google's Webmaster Tools:
The official name is "Sitelinks."
Sitelinks are completely automated, and we show them only if we think they'll be useful to the user. If your site's structure doesn't allow our algorithms to find good sitelinks, or we don't think that the sitelinks are relevant to the user's query, we won't show them. However, we are always working to improve how we find and display sitelinks.
From Google's Webmaster Tools: