HDDs, yes. RAM, no. After 2007 Apple changed the type of RAM used a couple of times. So don't count on RAM from 2006 being complatible with newer models. The 2006 model uses DDR2 667 MHz RAM while the newer models are using faster DDR3 RAM.
You can check what changed and when by looking at the tech specs at support.apple.com/specs/.
While your HDDs are reusable as Kappy said, be aware that the sleds they are in are not. The new Mac Pros use a different sled design so you'd need to take the drives off the old sleds and install them on the new sleds before you can install them in a new Mac Pro.
Also, you can get some good deals on the RAM you'll need here http://eshop.macsales.com/shop/memory/Mac-Pro-Memory#1333-memory.