From Shockley Consulting:
WebSearches is a script for the Big Cat context menu plugin (Big Cat is on VT already, and is also at http://www.ranchero.com/bigcat/). It adds additional web searches for highlighted text, but more importantly, it allows you to easily add your own web lookups, just by finding out the search URL. If you want to add a search to WebSearches, first run a sample search in your web browser. If the URL contains your search terms, copy the URL. Then choose ADD SEARCH in WebSearches' list, put in a name, and then put in the URL (making sure to REPLACE your search terms with ###SEARCHTERMS###). You've just added that web search.