tj: There should be a sticker on one of your door jambs indicating proper inflation pressure for the OEM tires. Inflating the aftermarket wheel/tire combo to that listed pressure should be sufficient to make it safe to drive. In general and as a guideline you typically don't want the tires inflated under 30psi or above 40psi (as measured after the car has been sitting unused for a while) on most passenger cars/SUVs. Since tire pressure varies due to things like ambient temperature changes and heat build up with driving, the pressure you set the tires at "cold" will vary by a few psi one way or the other as the outside temp changes and the tires warm up with use anyway, so it's more of an inflation range you need to worry about than an absolute single pressure on the tires anyway.
Regardless of which rims ( either stock or aftermarket ) are on the vehicle, stick with the vehicle's recommended tire pressures.
Look on the tire side wall for recommended pressure
Go to gas station or tire place