You can add a similar feature to Tiki 1.8.x as follows.
Note You will need to undo these changes before upgrading to Tiki 1.9 as Tiki 1.9 uses the same files but with different contents. Also beware that themes have tha ability to override these changes so you may find that the search bar isn't available on every page.
header.tpl - add at the bottom of the file:
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{* Site identity header section *}
{include file="tiki-site_header.tpl"}
create a new file - tiki-site_header.tpl - containing: