I'll first assume the soil is deep enough to support ornamental grasses. I'd say 18" minimum.

The easiest way to prepare would be to spray the grass with RoundUp or it's equivalent, to kill the existing grass.

Then mow/rake up the dead grass. Then all you have to do is dig holes, install the ornamental grasses, and mulch heavily between them.

The cheapest way to grow a large group of ornamental grasses is to grow them from seed. There's a wide variety of colors and sizes that grow well from seed, and are hardy in your zone. I'd start small ones to big ones, and just see what you like. Masses of grasses look great most of the year.

Hit the library for these books:

The Encyclopedia of Ornamental Grasses John Greenlee

The Color Encyclopedia of Ornamental Grasses Rick Darke

They'll show you hundreds of different grasses, cultivation requirements, etc..

Thanks donn for the start-up help -- I needed that orientation for the task before me. I will for sure check those books out. THANKS AGAIN!