The easiest way is probably heading to The Pearl and trying to arrange a threesome (or foursome if you're ok with including Zevran too) with Isabela. If Alistair or Leliana go along with the threesome then they're hardened. If not, then they're not.
I do have a script I wrote that will check Leliana's status and tell you if she's hardened or not. I also have a second script that will harden her if you wish. Modifying them to handle Alistair instead wouldn't take long at all. But you'd need to be comfortable with the console (see the wiki for the console if you don't know what I'm talking about here), and quite possibly the toolset as well to properly use them. I should also warn you that setting up the console for the first time is a royal pain in the backside. -Vim- 19:07, March 16, 2010 (UTC)