Hi Nick,
I hope someone has an answer. I looked at this a few times but I didn’t see any general solution – it seems to be one of those things that should be easy, but isn’t.
Here’s a blog post about various approaches:
http://www.alistapart.com/articles/multicolumnlists/
If you know in advance how many items you’ll have, and how many columns, then you can use a little PHP and hardcode the output in an HTML table – for example for 3 columns with 5 items per columns you can print item 1, 6, 11 across the first row, 2, 7, 12 across the second and so on.