Simple PHP button question

I have a very basic enter keyword, hit search button and produce result code. This is teh code for the form:

 
<form action="results.php" method="post" name="searchform" id="searchform">
  <input name="word" type="text" id="word">
  <input type="submit" name="Submit" value="Submit">
</form>

Which produces a simple submit button. Basically I would like to replace that standard submit button with a design of my own - so how do I get the button function to work on a gif?

Any help would be great thanks.:wasted: