The first thing to realize is you will have no screening for at least a third of the year if you use grasses. Ornamental grasses that tall will need to be cut to the ground in late winter/early spring, and will not regain mature height until summer.

That said, here are a few grasses which you can start from seed, will be hardy in your zone, and which will eventually reach the height you desire:

Sporobolus wrightii

Saccharum ravennae

Miscanthus sinensis

I'd suggest starting your clumps in cell packs or pots. This way you can install uniformly sized clumps. Use several or more seeds in each cell/pot to develop a thick clump from the start. Grow the clumps on in pots and install them in early fall.

There are many alternatives for more effective screening, including Willow and Hardy Bamboo.

That is very helpful donn, thank you. Someone once mentioned Hardy Bamboo but I know nothing about it. Is there any info you can share... can it be started from seed? What is Willow? thanks again.

The most common Hardy Bamboo is Phyllostachys aureosulcata, AKA Yellow Groove Bamboo. As far as I know, you can't grow it from seed, but it grows very well from transplanted rhizomes and clumps. Find someone with a local grove, and beg for transplants. This is a running bamboo, so you'll have to take that into account. It's best to contain it with bamboo rhizome barrier material.

Willow is Salix. Read all about it here:

http://www.bluestem.ca/willows.htm

Plan ahead for next year, and you can probably score all the cuttings you need for shipping costs only. I've got dozens of them growing from cuttings received from other Garden Webbers. The cuttings are usually taken in late winter, so it may be too late to get any this year. It couldn't be much easier to grow. You literally stick a foot-long cutting into the soil about 3/4 of the way, and it takes root instantly. You can count on at least 4-5' of growth, with several canes shooting from each cutting, in the first year.