This is for sidebar instead of header placement of the Show Me The Parts Search tool. 

Open w2m_showmetheparts.xml usually found here: /app/design/frontend/base/default/layout/w2m_showmetheparts.xml

Around line 35, look for the search placement reference line and change it to:

<reference name="left">
<block type="showmetheparts/search" name="showmetheparts_search" template="w2m/showmetheparts/search.phtml" before="side.menu">
</block>
</reference>

The highlighted portion is not mandatory. If there is more than 1 widget in the sidebar, this lets you specify that it should appear before that.