I'm not sure exactly what you want but generally when building a raised bed the walls should be set on virgin ground (not filled in soil) so the boxes don't shift or have the soil leak out.
In your case I might make a level footing from brick or other masonry material or I would just build the box from different sized wood. For example, make the up hill side from 2x8 and the low end from 2x12 or whatever would make up the difference in slope.
Hope this helps.

I'm not picturing exactly how you are planning to build your beds, but if your soil is properly amended with compost, it will hold a 60 degree slope quite well without much tamping. At the bottom of the garden, cut a V-shaped trench about 6" deep. This will help to prevent the grass from creeping back into your beds. It will be easy to rake any eroded garden soil out of this trench and back into the garden. I build my beds without frames, and only tamp the sides with my garden rake. It takes hurricane strength wind and rain to disturb them, and the rake is all it takes to rebuild them. Soil well amended with compost will absorb a lot of moisture before it starts to erode. A 1:20 slope should present very few problems.

Here is a link that might be useful: Trenching to manage grass encroachment

My first question is, How to tamp this soil well enough so it will hold its level after i build the boxes.

Second How to keep the soil from eroding until the grass regrows.

1. You can rent a tamping machine or buy/build a hand tamper.

2. I've seen lots of folks use straw/hay to cover their soil when planting grass. If you get it fairly level, you ought to improve your odds. Getting grass to grow on a hill can be a big challenge n seems those grass mats work best.

I think you have 1# answered.
2#, I would go around your hardscape,street,driveway & sidewalk, remove from 1/2 to 2 inches of grass.
Edge the hardscape & use the trim to sprig or plug the ground up to the trench.
Make sure all the roots are covered, but not the grass blades.
No air pockets under the grass & water once a day if it does not rain.
Good luck.

Here is a pic of my almost finished product. it is a facebook link so i am not sure if it will work. Not sure if i should just plant grass at the back of the bed to hold soil. or hosta or the like

http://www.facebook.com/photo.php?fbid=10150657535368911&set=a.10150441638193911.380981.817938910&type=3&theater

Hello again, I saw your picture(copied /pasted worked fine) and I'm just trying to understand why you mounded the dirt on the ground and then built the boxes on top of it. I have always understood that for optimum growing conditions one wouldn't want the soil compacted in/under a vegetable garden, raised or not.
What are you putting in the raised bed box?
Sorry I'm not any help but I'm trying to figure out why you didn't build the boxes right on the ground.
Hopefully someone else with a clearer mind can help.
Best of luck

It depends on how you want to manage that ground. Grass = mowing, but around the boxes it might be nice to have some lawn to walk on. For the sloped area, it might be easier to have a mix of perennial plants that will flower sequentially throughout the growing season - hostas being a good choice for a long-term base, if it's not too sunny all day - that will serve to hold the soil in place and eliminate the issue of mowing that particular area. If you do decide to grow grass, try to make the width of the slope the same as your mower deck, so you won't have to worry about scalping the sod at the top or the corners - in other words, make the design conform to an efficient way of maintaining the lawn. Be sure to use a thin mulch, or even just some fabric, on top of the soil if it rains before the plant roots start holding everything in place.