grouping groups?

Hi all,
I have a 'post' prototype with a date field (linked to a mysql table)  
- I want to be able to divide the posts up into an archive like:

year -> month -> day -> post

I thought about grouping the posts by year, then by month (children  
of by year) and then by day (children of by month)  - but I'm unable  
to use the groupname of a grouped collection in a filter statement ->  
I can't see the months in 2007 for example.

Does anyone have any advice how best to do this? Should I make an  
extra table or something?
It feels like it should be so easy - I must be missing something!

grts-
Jonathan