Welcome to the club.
The Supercharged option can be applied to any Lexus IS200 be it an S, SE or Sport. It is made by TTE (Toyota Team Europe) specifically for the IS200 and adds around 50 horses. A good mod, turning the sedate IS200 into the car it always should have been.
The Tezza comes in 2 forms. The AS200, which is the same as the IS200 (6 cylinder, 153bhp) and the RS200 (4 cylinder, 210bhp - 200bhp for the auto).
The imports do come with a lower spec (no leather or heated seats, less sound proofing, sat nav that won't work for example) but nothing that can't be sorted.
If you want tuning options and power out of the box, think about the Altezza. It needs to be revved harder, and insurance may be higher, but it's a good option. On the other hand, an IS200 is a UK car, may come warrantied, etc.
Horses for courses.
Let us know if you need any more help...