[IntegraX]

The Toyota Altezza and Lexus IS300 are the same body. From there, the seperation is mainly that the Lexus USDM version has a fleet of options and luxury setups you can get from the company, adding to the price, ofcourse. The JDM Altezza is essentially almost the same. The only difference is really what comes by default under the Lexus brand. You could put just about anything that can fit in the Lexus into the toyota. I'm currently trying to find a Altezza RS-200 L-Edition, and trust me, it's so hard to find. The majority are RS-200 Z-Edition, because in japan, it's all about performance. So it's much more difficult to find any luxury trimmed car with leather, and even sun-roof. Many are just flat, with all performance, and no leather or sunroof or interior panel trims. The performance package that Lexus sells you versus what you get in japan from TRD(Toyota Racing Development) are also different. Lexus is a much lower wing, and the TRD one is half that of a Type-R spoiler for example, and you also get body-coloured tail-light blockoffs and more for styling. The engine that is currently in the current generation of JDM Altezza is as follows:
RS-200 Z/L Edition ... VVTi 16V Inline-4 2.0 Cyl producing 210hp (MT) / 200hp (AT), and for AS-200 Z/L Edition ... VVTi 24V Inline-6 2.0 Cyl producing 160 hp for both AT/MT.
Currently, the Lexus IS300, is using a variant of the AS-200, but it's a more powerful Inline-6 3.0 Cyl. I do not know if it is faster than the 2.0 RS-200 from Japan. As you can see from the japan versions, the Inline-4 on the RS spec is much more powerful than the AS-200 spec. The AS-200 is the "Euro" model, while the RS-200 is the JDM version. You will find the same car in Australia as in USA, under a Lexus, contrary to Honda, which is only Acura in the Usa and Canada, and Honda elsewhere.