Here is an easy way to search a SharePoint site from the IE toolbar without having to develop a custom add-in.  Before showing you how to implement it, let's examine how custom search providers work.

How Custom Search Providers Work

When you browse to an Open Search enabled site in IE 7, the search provider drop down lights up

Provider Light Up

You can use a search provider temporarily while on the site (the yellow star indicates it's temporary), or permanently add it to your list of search providers

Temporary Search Provider

To temporarily use a search provider, click the provider name and the search box will change

Temporary Search Provider

To permanently add a search provider, click Add Search Providers and select the provider name

Add Search Provider

A confirmation dialog appears

Confirmation

After that, your custom search provider will remain in the list (note there is no yellow star) no matter which site you are currently on

Search Provider

When the users searches from the search box, they are taken to the SharePoint search results page

Search Results 

How to Implement A Custom Search Provider in SharePoint

To implement a custom search provider, create an XML file that describes it and place a link to the file on the site home page. 

Let's create the search provider XML file.  The XML is self-explanatory, with the key element being the Url.  There is a special token: {searchTerms} that will be replaced with the text the user types in the search box.  Note that the Url is absolute and will be different if you are using the MOSS Search Center (searchcenter/Pages/Results.aspx?k={searchTerms})

Search Provider XML

Upload the XML file to the Shared Documents library

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Place a link tag in the home page of your site.  You can put it anywhere in the page, but put it in the <head> element if possible.  The simplest approach is to use a Content Editor web part with the Chrome Type set to None

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That's all there is to it!

 

Summary

As you can see, implementing a custom search provider for SharePoint is simpler than a single-colored Rubix Cube.  If you would like to learn more about Open Search, the full specifications are available here: http://www.opensearch.org/Specifications/OpenSearch/1.1#OpenSearch_description_document.