I'm thinking of animating a WW1 tank over trench terrain, which given there's little in the way of suspension should be fairly straightforward, but I though there was a catippilar track interacting with bumpy terrain tutorial somewhere - anyone know where, I've looked and looked. If not any solutions, putting treads over wheels is fairly easy but driving them over terrain needs some trickery….

Not being exactly caterpillar tracks, but a transfer of an objects structure to the terrain. It's in Peter Quints video tutorials.

Atrtribute Transfer Pt. 1 [vimeo.com]
Atrtribute Transfer Pt. 2 [vimeo.com]

Maybe that is a good start for you…

Also check out this CMI-VFX tutorial on Procedural Modeling and rigging a tank including the tracks.

http://www.cmivfx.com/tutorials/view/153/Houdini+Intro+to+Procedural+Modeling [cmivfx.com]

I also just posted a file on another thread this morning that shows how to use the Carve SOP to animate points along a curve and then copy stuff to it.

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=100726#100726 [sidefx.com]