The google home page displays the logo after the
with an id lgpd. The tag after this is the one that displays the festive logo image of google. The greasemonkey script would have to fetch the google home page, navigate to this br, and pick up the entire tag.
The homepage could be fetched using GM_XMLHttpReque
This tag would then have to be substituted inside the tag that has the id "logo", that displays the original google logo. Hence, the logo on the google home page would be on the search page. The size sure would be a problem but that can be fixed by using the same tag as span that has the original google logo as its background image.
Watch out this space for the script details.