making Flower bed boxes

[vfig777]

Ive got a customer that wants flower bed boxes installed in front of her house. She wants to use large landscape timbers. Should I use the pressure treated timbers at a homedepot (largest they have is 5 1/2x 5 1/2) or is there something else I should look into.
2nd question
What is the proper way to install the larger landscape timbers? Should I bury the first layer like I would when doing a stone wall? Do I bury a 4x4 post into the ground so I can attach the timbers to that (so the wall doesnt cave in or out)? If so, do I use cement or just back fill with dirt and pack it good? If I do use post, how far up should the post be exposed?, flush with the top of the wall or should it end 1 layer short of the top so that its covered with dirt and mulch?

Thanks

[LindblomRJ]

How high a bed are they? I would make sure the first row is level. What I did on my own personal flower beds was level it up. Stagger the joints. The tallest part was 4 rows of timbers. I drove a spike (like 3 per timber) into the ground. Then used "pole barn nail" 60p to secure the rest of the timbers to the first row.

Mine are preasure treated.

I sure you will hear of a better way to do it. I am willing to learn. It looks good at my house at least.