I eventually got what I needed here from Nick Momrik's http://mtdewvirus.com/code/mdv-archive/ (found via podz http://www.tamba2.org.uk/T2/).
You probably know to save your old files (in this case, archive.php I think, and if you want to do the same thing for search results, search.php. Looks like they download as text and you rename them. I say "looks like" because it's been a while!) Anyway, in this case, you'll definitely need the old files, to pilfer code for tweaking. Momrik's code gives you the whole month on an archive page, but only the titles. What I did (inspired by Podz, but [wheee] I figured it out on my own) was to go to the original files where some of the options (month, week, etc) are set to show excerpts as well. Nabbed that code and edited the Momrik file and I've got a month of partial entries on one page at least.
I would imagine that a bit more industriousness could similarly give a month of full posts if that's what you want. This is as far as I went for what it's worth.