I was hired to write a review about blackjackpractice.org which purportedly blackjack practice, however I wasn't able to verify this, since the site is down (currently it is showing a default directory listing from Apache, earlier today it was showing an empty page). There is very little know about this by the usual sources, and there doesn't seem to be anything interesting on the same server (it is hard to tell if the same person owns all the domain on the server due to the "privacy protected" registration).
Now back to the idea to blackjack practice: can you really train yourself? Probably, to some extent (hey, even Kent Beck - yes, that Kent Back - has a poker training website). With regular exercise you can memorize basic strategy table (this will help you with any game, regardless if its with a live dealer or with a machine - supposing that the machine is playing fair) and then you can move to more advanced techniques like card counting or shuffle tracking. I doubt however that you can achieve a level where this would be a profitable endeavor.
Full disclosure: this is a paid review from ReviewMe. Under the terms of the understanding I was not obligated to skew my viewpoint in any way (ie. only post positive facts).