Search Engine

How to I create a Search who is built up in this way:
You have a text-field and a Select field (scroll down). I want the script to read the option in the text-field and search through a different URL per choise. If you f.ex chose AltaVista it will search the query through altavista.com/search&query.cgi or anything, but if you select Yahoo it will search through another. Just type CHOISE1, CHOISE2 e.t.c and URL1, URL2 e.t.c.