If anyone is interested, I've more or less settled on using Typo3. It's the only CMS I've been able to find that can do everything we need. I've worked with Mambo for a few days, but I'm getting more and more frustrated with it. The latest version 4.5.1 is buggy as hell, the menu system is confusing at best and it outputs horrible markup that you can't change without breaking the upgrade path. Typo3, here I come! I just printed out the "Getting started" document - all 118 pages of it!
"Programming is like sex: one mistake and you have to support it for the rest of your life."