For IE7

 

You need to delete History

Open Internet Explorer/Tools/Internet Options/General

Under Browsing History click "Delete"
Then click "Delete History"

 

You will have to do this every time you have used the machine on the internet.

But I dont wanna delete the visited websites, as that is very helpful. Just what I searched.

OK

 

I think this is the only way to do it
http://ask-leo.com/how_do_i_clear_my_search_history_in_ie_7.html