Frank is right. You don't need the URL bb code for images, just the IMG code. Be sure you're clicking the correct buttons, Eliot. My apologies if you already know this, but here are the buttons to use for:
Posting Pictures:
Click this, and a little dialogue box opens. Paste the URL of your image and hit the Insert Image button and you're golden.
Posting Links:
Click this, paste your URL, and hit the Insert Link button. The default link text is "My Link," but if you want to use your own words, either type them in the Link Text box below the URL box, or type your text in the Post Editor field, highlight it, and then paste your URL in the appropriate box. Works either way.
Posting Video/Audio:
This works best for YouTube videos, but you can also post MP3s if you have a direct-link URL as I did
IN THIS THREAD.
When I first started using HuskerBoard I was not a fan of IP Board. I'm used to phpBB, and most of the other forums I frequent use it. But as time wore on and I got more used to IP.Board, it's pretty clear that it's a far better product. More agile, more useful, and far easier.