I found a plugin that would work perfectly to allow visitors to show posts that match multiple categories (example, show all posts that are in both category 1 & 3, but not posts that are only in 1 of the 2 categories)
Advanced Multiple Category Plugin
Unfortunately, it doesn't work with pretty permalinks, which my site uses. Can anyone take a quick look at the code supplied on the above page and (hopefully) suggest how I can make it work with pretty permalinks. Thank you!
p.s. sorry about the multiple posts 20 minutes ago... when i submitted the first post, i received a message that led me to believe it hadn't been posted. and now i cannot reply to either of the 2, so I'm starting this new thread.