If you are using Internet Explorer drag any of the following links (choose the desired language pairs) into your Favorites. If your Favorites are not visible on the left side of your browser, go to View->Explorer Bar->Favorites. Users of Mozilla Firefox need to drag the link onto their Bookmarks Toolbar (View->Toolbars->Bookmarks Toolbars) and Opera users onto their Personal Bar (View->Toolbars->Personal bar).
Double click on word to select it. Then, single-click the button (Firefox, Opera) or link (IE) of the corresponding language pair to translate the word in the same window. If you forget to select a word, a text input field will be displayed. See this
screenshot of bookmarklets in Firefox.