I did some more work using the Rico and Scriptaculous libraries today and I came across two things it might be useful to know:

1. IE treats the name attribute on form fields as if it was an ID, Firefox doesn't. It took me a while to figure this one out, I was wondering why the autocompleter was working on IE but not on Firefox, and it turned out to be this problem with the HTML our legacy web app was outputting. Probably everyone knows this already, even I had heard about it before, but I spent a lot of time looking for javascript errors before I figured out it was a basic HTML problem.

2. You can use both Rico and Scriptaculous but you have to include the rico.js before you include the scriptaculous.js (and both after prototype.js). If you put rico.js last then you'll get errors with creating the Rico.Effect library. This may change - I am using beta or release candidate versions of both libraries, and there might also be some more advanced conflicts I've not seen because I'm only doing simple stuff.