Dropdown sort by month and cat?

Hi,

I put the followering code into my index.php:

<form name="archiveform" action="">
<select id="m" class="formElement" name="archive_chrono" onchange="window.location =
(document.forms.archiveform.archive_chrono
[document.forms.archiveform.archive_chrono.selectedIndex].value);">
<option value=''>Monat auswählen</option>
<option value='<?php get_cat_ID() ?>'>Alle Monate</option>
<?php get_archives('monthly','','option'); ?>
</select>
</form>

Now I search for a solution to sort the different cats by months, so that I can search with the dropdown-menu only in one month and not in all.

Momently I click on the Month and the reason is this:
… .de/?m=201001

And this is the reason by click on the different categories:
… .de/?cat=1

But I search for something like this (for example in january 2010):
… .de/?cat=1&?m=201001

I hope anybody could help me.