Welcome to the club matey
Heres some info on the wheel and tyres sizes [url="http://www.lexusownersclub.co.uk/forum/index.php?showtopic=637"] [b]CLICK ME[/b] [/url]
Theres also a wheel offset calculator [url="http://www.1010tires.com/WheelOffsetCalculator.asp"] [b]HERE[/b] [/url] To help you with the sizing of new wheels,
The et 38's will sit 3mm further in than Ormi's 35 offset above, but the 255/35/18 tyres i would say are too wide for the IS200 as the reccomended tyre size for 18" wheels is 225/40/18
The 38 offset in a 7" wide wheel 18" diameter will give you 7mm more clearance from the strut and extend 7mm further out,
With a wheel 8" wide and the offset 38 will give you 6mm less clearance from the strut and extend 20mm further out?
(compared to the standard 17" wheels)
Ormi above has 8" wide with an offset of 35 and compared to the oem wheels give 3mm less inner clearance and extend 23mm further out