Switch1 on the newcelica.org forum had his engine seize too. He misshifted and overreved the engine, then when toyota repaired it, they stuffed something up then it seized a few weeks later. They quoted him a fortune to fix it.
He ended up getting a complete new engine for 2.5k. Best of all it had only had 800m on the clock!!!
The place that sourced the engine for him was called Bezerkly automotive (http://www.bezerkly.com/) and that may be your best bet to get things sorted if your car is not under warranty :)