iPad Detection
You should be able to detect an iPad user by taking a look at the userAgent property:
var is_iPad = navigator.userAgent.match(/iPad/i) != null;
iPhone/iPod Detection
Similarly, the platform property to check for devices like iPhones or iPods:
function is_iPhone_or_iPod(){
return navigator.platform.match(/i(Phone|Pod))/i)
}
Notes
While it works, you should generally avoid performing browser-specific detection as it can often be unreliable (and can be spoofed). It's preferred to use actual feature-detection in most cases, which can be done through a library like Modernizr.