You can also go to http://wargameroom.com/. They have a free TS module, but it is a little trickier to install than Vassal (but it is a little more stable).
I learned on wargameroom, but that's the hard way. It's not nearly as newbie friendly a way to learn the game as steam, mostly because the card language is not readily visible. The players there are also much more experienced in general, so you'll have a more difficult time finding an opponent near your level and likely speed of play (i.e. slow).
I was playing TS on Steam using my older iMac - it worked fine until about two weeks ago when it went into glacial speed mode. Has anyone else encountered this? I've tried reloading to no avail. The Playdek/Steam folks won't respond to my requests for help.