I'm clearing out some of my templates and had this in a test page. I don't know if I ever posted the code here, so just in case I hadn't, here's the code to create a dropdown "jump box" that will forward you to the selected month's archive.
(Script assumes you are on MT. No php needed here – this one is all javascript)
<form name="jump2">
<select name="myjumpbox"
OnChange="document.location=jump2.myjumpbox.options[selectedIndex].value">
<option selected>Please Select…</option>
<MTArchiveList archive_type="Monthly">
<option value="<$MTArchiveLink$>"><$MTArchiveDate format="%B %Y"$></option>
</MTArchiveList>
</select>
</form>
kind of like this: