I believe tires with that size should fit without any problems. Keep in mind that size has an outside diameter that is 2.5% larger than stock, so your speedometer will read 2.5% slower than you are actually going. This will also throw off your odometer by 2.5% as well.
Also remember that wider tires will have more friction and your fuel economy will suffer a bit.
The ride quality will suffer too because of the 18" tire's short sidewall height.
However it will probably look very cool. You need to get a wheel with the appropriate offset and width in order to fit into the wheel well. You should get a wheel with a width of about 7 inches and an offset as close to 45mm as you can.
Good luck and let us know how it goes. I wouldn't mind seeing pictures of your mod too!!