I haven't made any, but it's my understanding of the process that you first cure the brisket to make corned beef. Then soak the brisket in several changes of water to remove the salt. Finally add the dry rub and cook to 180*.
David,I just made pastrami using Emeril's recipe.Just go to Food network.Go to his page,type in pastrami.Scroll down to beef pastrami.Man this was some good stuff.If you use this recipe,and can't find juniper berries let me know.A guy from another site sent me some,and I'll send you some.Since than,I found them at Safeway.The only problem that I had was waiting the three weeks,while the brisket was in the mariande.But it was worth the wait :D Hope this helps.
I've only made them from whole packer briskets, trimmed seperated flat/point cuts, and brine-cured with Morton's Tender Quick and a few of my personal recipes. Never used any store-bought corned beef, myself, as I can control the flavor profile much more when I cure my own.