<FORM>
<SELECT ONCHANGE="location = this.options[this.selectedIndex].value;">
<OPTION VALUE="side1.html">side1</OPTION>
<OPTION VALUE="side3.html">side2</OPTION>
<OPTION VALUE="side3.html">side3</OPTION>
<OPTION VALUE="side4.html">side4</OPTION>
</SELECT>
</FORM>