When you use the search field in Safari on iPad (or iPhone), Google is used to search the web, by default. If you like, you can change the default search engine in Safari to use Bing or Yahoo!, instead. (Requires iOS 3.2.1 or later.)
Open Settings. Next, tap Safari (in the left column) and then tap Search Engine. You will see Google, Yahoo! and Bing listed. Tap the one you'd like to use.
Now, when you type something into the Safari search field, the search engine you had selected will return the results - from Google, Yahoo! or Bing.