How do you use basecamp's fairly rigid tools for facilitating the scrum PM framework?
I used basecamp with scrum for over a year. It was wonderful and I wish I could go back.
Excellent writeup here how to do scrumxp with basecamp The key ingredient is the burndowngraph.com tool.
With modifications to that, here's how we ran it...
I kept one todo list as the product backlog. (When things were very crazy at first, we used a spreadsheet, but use what works for you). For those that required more description we would use the comments to add what we needed. Normally this was acceptance criteria, mockups and "gotchas" that we didn't want to forget about.
During each sprint planning meeting, we grab the stories from the top and break each out into its own todo list. Then for tasking we would create a todo item for each task and use the "6h" method of marking the estimate so burndowngraph.com would pick it up.
Sprint planning summary, retrospective, and items completed were all logged as messages. For very detailed items, we would sometimes use a writeboard to log the "spec". An attached word doc would work just as well.