Большое спасибо Ruslan_xDD!
Получилось как-то так, все работает:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title></title>
<style>.table {border-collapse: collapse; border: 1px solid #00280e}</style>
</head>
<body onload="document.getElementById('frame1').src = document.getElementById('select1').value">
<table align = "center" bordercolor = "black" border="1" class = "table" width = "1065">
<tr>
<td colspan = "3">
<img src = "pict.jpg">
</td>
</tr>
<tr>
<td rowspan="2" width="230">
2
</td>
<td width="605">
<select id = "select1" onchange="document.getElementById('frame1').src = this.value">
<option value="Table1.html">Table1</option>
<option selected value="Table2.html">Table2</option>
</select>
</td>
<td rowspan="2" width="230">
2
</td>
</tr>
<tr>
<td>
<iframe id="frame1" width="605" height="150" src=""></iframe><br/>
</td>
</tr>
</table>
</body>
</html>