Thanks for the info — I had looked at this technique as well but wasn’t sure. Added the line to my .htaccess file, but it didn’t work.
One important piece of information i forgot to add in my initial request: the site is built in WordPress, so I’m attempting to add the download links in posts. I don’t know if that makes a difference, but thought I should mention it.
Update 4/13/10: I really, really hope someone out there will take pity on me and offer some help on this one. I suspect it has something to do with the fact that I’m attempting to do this inside a WordPress post: no matter what I do (including one attempt to use php to force a download) clicking on the file link just tries to open a new page. I’m due to hand the project over to the client tomorrow and would really like to have this issue solved before then.