It will definately needs a larger tank than that, Clown tangs are notoriously agressive, especially to any new addtions to the tank. Generally if you want to keep one, it would be the very last fish you add to your tank. Do you live in ChCh by any chance?
There are several reasons why Clown tangs are considered difficult to keep. First they are often caught with cyanide, meaning they die slowly of cyanide poisoning. And second people do not feed them the correct diet. Like all tangs, they are heavy feeders and require a lot of vegetable material to remain healthy.
If you get these two problems sorted they are not particularly diffucult to keep. But yes, it will require a larger tank. I think a 6 foot tank is minimum for the optimum lifespan of the fish.
Layton