Originally Posted by tejaswi.rohit

Xcode is a 64bit app so It can't be run on our 32bit only Lion. You can install Xcode 4.2 but you will have to change the system version before installing by editing a file. You will have to do that every time you run Xcode and or you want to restart. Basically you have to spoof that your OS X is 10.6 to run Xcode 4.2 on Lion. and don't forget to change it back to default when you would like to restart else OS X won't boot.