The Spanish Oak processors in the new S197's are very tempermental when it comes to messing with the a/f mixture.
Your 03 will do just fine with a CAI and no tune. Just disconnect the battery before the install and after you drive for a while it will settle in. You should consider a plenum/ TB combo next for a nice, crisp throttle response.
You can always get a handheld tuner down the road and either have a custom tune made for your mods or use a canned email tune. They'll generally squeeze a bit more power out of a stock set up but not as much as on an S197.
Do you have your eye on a specific CAI? I installed the generic 96-04 model CAI from American Muscle (only like $85) and it looks and performs great. All the major names make great CAI's but a lot of times you'll be paying for the name.
Just an fyi... 
__________________ 66 Coupe Tahoe Turq - 200, Pertronix & Flamethrower, 3 Row Rad, Cliff. 6/2 96 GT Vert Laser Red - FMS pulleys, Bullet ProM, BBK CAI, Prof. Prod. Elbow and 70mm TB, MAC Off-Road H, Borla side exhaust, Tokicos, B&M Ripper, 18x10 & 18x9 DD Bulletts 06 GT Tungsten, UIP, Red Leather, Stick, 18" blades, Steeda CAI, SCT XCal 2 w/ MC Racing 91 tune, MACs, BMR SP010 springs, BMR Adj Panhard, CDC ducktail & quarter louvers, Rear louver, painted black stripes |