Dear jasonF ,
Unfortunately you can not add layouts for archive page. It's next major feature for layouts, but right it's not implemented.
I can not say when it's will implemented, i know only that this will added in next layouts release.
for now you can try:
1. Create dedicated file for each archive page
example category_slugname.php
2. Add layouts using php
More info:
http://wp-types.com/documentation/user-guides/layouts-theme-integration/
http://codex.wordpress.org/Template_Hierarchy
Please let me know if you are satisfied with my answer and if I can help you with any other questions you might have.
Regards,
Gen.