"Am I running on iPhone? or WebPlayer? or Win32?" detecting it on runtime?

http://unity3d.com/support/documentation/ScriptReference/Application.html

and

http://unity3d.com/support/documentation/ScriptReference/RuntimePlatform.html

 switch(Application.platform) {
    case RuntimePlatform.WindowsPlayer:
       // Windows specific code
       break;
    case RuntimePlatform.WindowsWebPlayer:
       // Windows webplayer code
       break;
    case RuntimePlatform.IPhonePlayer:
       // iPhone
       break;
    case RuntimePlatform.WindowsPlayer:
       break;

}

If you want to detect if its WebPlayer (and don't want to differentiate between MacOS/Windows), you can do

 if(Application.isWebplayer) {
     // is playing in webplayer
 }