In Windows 8 by default Bing has been set as the default search engine for IE 10 in metro and desktop environments and its the only search provider Internet explorer offers in Windows 8 Consumer Preview, if you want to set Google as default search engine in IE 10 first you need to add it as a search provider which you can do from IE Add-ons gallery page.
Adding Google as a Search Provider in IE10
Visit the link http://www.iegallery.com/en-US/Addons/Details/813 in desktop IE 10 and click on “add to Internet Explorer” once the Google search add-on page has been loaded from Internet Explorer Gallery site.
Now a dialog pops up asking you to add Google as search provider, in that dialog check or select make this as my default search provider and click on “add” button.
That’s it from now onwards Google is the default search engine in Internet explorer 10 in windows 8 for both metro and desktop versions.
You can see Google listed as search provider under “Search Providers” for IE’s “Manage add-ons” window and you can also see Google icon along with Bing icon when you click the search icon in the IE ‘s address bar.