Question
I HAVE A SLIGHT HILL THAT RUNS ALONG A 1/2 OF A QUARTER MILE. NOT VERY LONG BUT LONG ENOUGH.QUESTION- I WOULD LIKE TO ROTOTILL ALONG THE LENGTH OF THE STONE WALL DOWN TO ABOUT 8 FEET. THE AREA IS A MESS WITH OLD GROUND VINES AND SUCH.  I CAN'T AFFORD A PROFESSIONAL AND WANT TO TURN THIS INTO A SHRUB BORDER. PLEASE ADVISE ME ON PROPER USE OF A ROTOTILLER.HOW TO DO IT WHEN AREAS HAVE DIFFERENT RIDGES.  I PLAN TO PUT IN FRESH TOPSOIL WITH HEALTHY AMMENDMENTS.  PLEASE ALSO ADVISE ON PREVENTING EROSION DOWN THE HILL. THIS NEEDS TO BE DONE ON A VERY LIMITED BUDGET.
THANK YOU FOR YOUR HELP.

Answer
Proper usr of a rototiller can be found at:
http://www.ehow.com/how_4235_rototiller.html?ref=fuel&utm_source=yahoo&utm_mediu...

They come in different sizes and for larger jobs, attached to the back of a back-hoe.

As far as the SIZE of the job (if I did my math correctly), 1/2 of a 1/4 mile is 660 feet, or about 2x a football field.  At 8 feet wide, x 660 feet, that is approximately 5,300 sq. ft.

As to amended soil, great.  At 3 inches deep, x 5,300 sf, you're looking at 49 cubic yards of soil! (about 3 LARGE truckloads).  Wow.
At $12-$14*/CY, thats about $600-$700* that might not do much in the end.  Plus, moving this amout of soil without mechanical help (a back-hoe) is a major job with just wheel burrows.  

*Prices are VERY sensitive to your location and how far it has to be trucked.  These are just estimated numbers. Check locally with a bulk supplier.

That Back-hoe with a rototiller attachment, though expensive to rent, might be the better option, assuming it is as big a job as I've figured.

I think that once you get the old growth out, and rototil it all up, the exsiting earth will look great and able to support your beds, even without the added soil.

As far as erosion, plants roots do a dandy job of keeping things put.  Since I don't know how steep a slope we're talking about, I cannot give you specific recommendations.  

In some areas a "gentle slope" is 4:1 (1 foot drop in 4 feet of "run"), which is about what you can get by without extra treatments.  It also depends on how much RAIN you get, and in what quantities (6" all at once, versus over the entire year!)  

If you are concerned, there are inexpensive mulches you can add, like straw or seed-free hay.  Rocks/gravel work well, too, but then you get into a larger outlay of cash, as they usually costs more than just top-soil.

Hope it helps.  ~Marc