You will need to kill the grass before making a bed. Do a search here on GardenWeb for 'lasagna bed', that may work for you, or use a herbicide.

Unfortunately, no groundcover will prevent all weeds. You will have to weed, but less that bare ground. Liriope spicata- running liriope gets thick enough to keep down most weeds, but it can also take over you lawn, and it needs a "haircut" with a weed wacker or mower in early spring.

Crown vetch likes well drained soil and full sun. It has a pretty bloom, too.

I am gradually increasing the coverage of our yard with creeping thyme. (taking transplants from heavy areas each year) It smells good when I mow, doesn't demand a lot of water, grows in poor soil areas, and seems impervious to disease. True it doesn't "Green-up" quickly in the spring but that isn't a concern to me.

I am thinking of replacing all our grass with moss. Of course most all moss preferes the shade, but Is there a type of moss that does well in full sun?

I've had very good results with creeping sedum as a groundcover in full sun on a slope. It's very easy, spreads nicely, easy to propagate, and needs little care.

However, I would get the grass up somehow before planting anything. It will save you work in the long run.

Good luck!
:)
Dee

I forgot to add that the sedum I have, Weistenphaner's (sp?) Gold, turns a beautiful burgundy color in fall and stays that way throughout the winter.

:)
Dee