I wasn't specifying the width of the cell which was the problem: adding the bold stuff made it work.
Code:
<table width="100%" border="0" cellspacing="0" cellpadding="3">
                <tr>
                  <td>
                    <form name="searchForm" action="http://www.google.com/search?q=site:turtletips%2Ecom+">
                      <br>
                      <script language="javascript">
					  <!--
					  	function transferKeyEvent()
						{
							if (event.keyCode == 13)
							{
								event.returnValue = false;
								submitSearch();
							}
						}
					  // -->
					  </script>
                      <input style="width:100%" type="text" onKeyPress="transferKeyEvent()" name="q">
                    </form>
                  </td>
                  <td width="75"> 
                    <div align="right"><a href="javascript:submitSearch();"><img src="searchbutton.jpg" width="70" height="27" border="0" align="absmiddle"></a></div>
                  </td>
                </tr>
              </table>