1.Login to your blogger dashboard--> layout- -> Edit HTML

2.Scroll down to where you see </head> tag .

3.Copy below code and paste it just before the </head> tag .

<style type='text/css'>
div#search { background: transparent url("http://3.bp.blogspot.com/_4HKUHirY_2U/SwZCwFFG_yI/AAAAAAAAAQ0/ulhHnhO8ruI/search.gif") no-repeat scroll left top;margin: 0; width: 320px; height: 44px; }
div#search form { height: 44px; }
div#search form p { display: block; margin: 0; padding: 14px 0 0 30px; }
div#search form p input { width: 285px; border: 0; background: transparent none; color: #ffffff; }
</style>

4.Now save your template.

5.Go to Layout-->Page Elements and click on "Add a gadget".

6.Select "html/java script" and add the code given below and click save.

<div id='search'>
<form action="http://YOURBLOG.blogspot.com/search" id='search form' method='get'>

<p><input id='searchform' name='q' onblur='if (this.value == &quot;&quot;) {this.value = &quot;Type your search here...&quot;;}' onfocus='if (this.value == &quot;Type your search here...&quot;) {this.value = &quot;&quot;}' type='text' value='Type your search here...'/></p>

</form>
</div>

Note : Replace "YOURBLOG" with your blog name.

You are done.Look at the picture below.

Search Box For Blogspot Blogs