Drag the bookmarklet you like to your browser's bookmarks toolbar (to enable in Firefox: right-click on menu bar, check "Bookmarks toolbar"; in Chrome: Wrench/Tools/"Always show bookmarks bar"). If you then click on the bookmarklet, a box will prompt you for search terms, and the results will appear in new windows/tabs. If you first select some text with the mouse and then click the bookmarklet, the search starts right away without further prompting.
In Firefox and Chrome you can also directly search from the address bar with a keyword, which is my preferred method: go to the address bar (Ctrl-L), enter a keyword followed by a space, search terms and Enter. To assign a keyword to a bookmarklet: in Firefox right-click on the bookmarklet, choose Properties, and enter the keyword. In Chrome it's a bit harder: right-click the bookmarklet and choose Copy, then Wrench/Options/Basics/Search/Manage/Add, enter a name and keyword and paste the bookmarklet into the URL field.
To quickly get rid of the opened tabs: Ctrl-W.
Here are the bookmarklets:
All these scripts are in the public domain; you can use them in any way you like.