I want to install XCode 4.2 on my mac. I have the dmg, but when I start the installation process, I get the file size as zero kb. Attaching the screen shot of the same:

Can anyone tell me what the problem might be???
The Mac version i am using is 10.7.2….
I have tried changing the install location, but it was of no use.
The installation process takes around 15 mins (although the size is zero kbas is in screen shot) and at the end, I am getting the message “Installation Completed”


EDIT:
For mac OSX version 10.7.2 (Mac OSx Lion), Do I need to download XCode 4.3. The dmg that I have got from one of my friend is titled “xcode_4.2_and_ios_5_sdk_beta_6_for_snow_leopard.dmg”. Also, I have tried installing XCode 3.2.6 and it also is experiencing a similar problem.
I have downloaded the new dmg of XCode 4.2 from apple developer portal (developement tools). Its XCode_4.2_for_Lion. And it has got installed without any problem.