Yeah I think they fit fine if you're on standard suspension don't they? You could use a lower profile tyre perhaps - I think 255/35/18 would give you the closest match in overall wheel diameter to the standard 17s on 215/45/17.
On a separate note £40 for a set is an absolute bargain! How did you manage that? Are they in decent condition?
2002 '02' IS200 SE Auto - DVD Satnav with Voice Activation - [COLOR="Blue"]Strathcaron Blue - Parking Sensors - 5000K HIDs with Anti-Glare Bulbs - PIAA 6500K Main Beams - LED Sidelights - Mirror/Sunroof Closure - TTE Styling Kit - 18" Styling Kit Alloys with nitrogen filled Goodyear Eagle F1 Asymmetric Tyres - Bluetouch Multimedia Kit - Gromaudio AUX in - Black painted calipers with silver Lexus decals - 12 LED Dome Light - 96 LED Boot Light - Stainless Steel Sport Sill Plates - PIAA Silicone Wipers[/COLOR]