I've had my 2006 HCH II since March, 2006 and just installed the small fender mud guards. They cost about $95 for the set of four. Pretty easy installation - here are a few hints:

1. When you buy them, make sure you ask the Parts department to print out the three pages of instructions. They are NOT included in the box of the actual parts.
2. The instructions are very well-written and clear. Don't make fun of the push pins - they are really useful (if you don't understand this comment, wait until you read the instructions!)
3. BIG recommendation - before installing the rear fender mud guards, get out the tire jack and remove each wheel. It makes installation a LOT easier!

Including the time it took me to remove the rear wheels, install the guards and put the rear wheels back on, I estimate I spent 2 hours on this project. The mud guards look great, BTW.