After much pre-publicity,  DNA Ancestry is finally here.

Since I haven't tried this yet myself, and it's pretty much news for all of us, I know about this much:
You buy a kit, swab the inside of your cheek, just like in the CSI shows, send it back to Ancestry and they will process your results and mail them back to you.  Your results can also be added to an Ancestry database to be compared with other people's results or be kept totally private.  DNA matches are communicated anonymously.

Please open this user-friendly pdf and read all about the process.  They say it as well as it can be said.

And/or click the following link and read about it there.