If I understand your question, that would be: Internet Options¦Content¦Autocomplete Then un-check the Forms and User names and passwords on forms checkboxes. You can access Internet Options from Control Panel or from the Tools menu in IE.
You can use Clear Search History in the pull-down menu next to the Google logo in the Google toolbar to clear the toolbar search history.
If your reffering to the pulldown form/box, when you type in a letter the box will open-under and suggest a search keyword, etc. Highlight the previous search terms in the open-under areas and hit your "delete" key. You may have to enter all letters in the alphabet to expose all the saved search words/terms.
I may have misunderstood the question here, however to clear the search history, simply click on the Google logo on the left of the search bar in your toolbar. about halfway down and it says "Clear Search History"