If you want to do this without changing any code, you could use a tiny plugin I made a while ago. It makes WordPress think that order=ASC is always in the URL, so all archives end up in ascending order:
http://www.myelin.co.nz/post/2006/2/24/#200602241
Here’s another thread about ascending date order in archives:
http://wordpress.org/support/topic/10355
I’m sure there’s an easier way, but I’ve written a (VERY) small plugin to do this.
Download from here: http://www.myelin.co.nz/post/2006/2/24/#200602241
Install and activate the plugin, and from then on your archives should appear in ascending order.
