Bookmark the following link (right click, "Add to Favorites") and you can search any page by going to that page, and then clicking the bookmark you make of the link below. The script will pop up a small window into which you can type your search term, and then see Google's results for that page.
Search Current Site (IE/Opera/FireFox)
For the really lazy like myself, this version works by using whatever text you have highlighted in the page as the search term.
Search Current Site (IE/Opera)
Search Current Site (FireFox)