Also, if he asks why TamaTalk was blocked on the school computers, tell him that it's because it's got nothing to do with school work! That's what our school has done... it's blocked just about everything... including UNblockers! I can't go to MSN Webmessenger, I can't go to MySpace, I can't even go on FreeWebs and edit my homepage! But it's for good reason, so that I actually get some work done during classes. That's why they've probably blocked it.
Also, with most school blockers, they block KEYWORDS, not websites. That's probably why websites like MySpace and FreeWebs, and yet sometimes when I'm researching something and I click on results that are shown on a FreeWebs website, I can't view it (it's a royal pain for studying, trust me!).
But like others have said, the best thing to do is wait, and see if he's blocked it or not. And if he has, then ask him kindly, with lots of pleases and thank-yous, if he can unblock it. Take him to the computer, when he has time, and show him what it is, bring up a couple of topics maybe and show him that all this is is a Tamagotchi fansite. This is probably one of the best, most organised, most loving! forum websites I've ever been on, now I think about it. Tell him that! I'm sure he'll listen, and I'm sure he'll unblock it.
Some advice though, don't approach him if he's in an angry mood! I know from experience that parents, when angry, just don't listen at all, and it seems unfair. If he gets that way with you, just back off, let him get over his mood, and approach him the next day. It works!
Hope I helped somewhat!