Hi Heather,
It sounds like you might be trying to target the source code of the Smart Searchbox web part. If so, it would be best to clone this web part and then review the source code in Visual Studio. You'll get an understanding of how it work and what IDs relate to which controls.
For your reference, the IDs are:
lblSearch (the label)
txtWord (the search textbox)
You can review the original source code below, but I would strongly recommend cloning the web part if you're planning on making any changes:
\CMS\CMSWebParts\SmartSearch\SearchBox.ascx
\CMS\CMSWebParts\SmartSearch\SearchBox.ascx.cs