Based on your code above it looks as if you have a "bar" the length of your table. Is that correct? Are you trying to place the search box on top of this bar or do you want the image to be the submit button?
If you want the text and box to go over an image just created a table and set the background there but don't specify a background in the individual td unless you have a button that you're putting the text over.
I hope I caught what you wanted and this made some sense
