First, check the default search template code: design/standard/templates/content/search.tpl and searchresult.tpl. On this template, you may have something like:
Thanks Jean-Luc Nguyen for taking out time for my post.
but had no luck with searchresult.tpl.
Whatever changes i does on search.tpl or searchresult.tpl. is not viewable on frontend, and there are no override files for them either.
as far as i have studies the code, ezpublish uses ezwebin/design/ezwebin/override/templates/line and files in it to show search result, for folder it will use folder.tpl and for article it will use article.tpl.
what i want is a common script to highlight the searched word (both in heading and in description)..
I think that before trying to highlight your search results, try to override default search templates; do not edit design/standard/templates/content/search.tpl and searchresult.tpl, but override them by creating them on your extension, something like extension/your_extension/design/your_frontoffice_design/templates/content/search.tpl and searchresult.tpl.