If it downloaded correctly it should be in your appdrawer (default position of the button for that is in bottomright corner of your home screen, the blue button with 4 white squares in it), then scroll through the pages left or right to find your application, if it's not there, it's probably not downloaded correctly. I have found a couple of Market issues with my Ace, sometimes it doesn't start downloading properly and I have to hit the download button again, in the top status bar you can see if an application is being downloaded, finished or installed.

 

I faced same problem and downloaded angry birds four times, but no use. It only increased my airtel mobile bill. I downloaded angry birds APK file from other sites (google it) and installed it. Worked fantastic.

Download APK file into SD card and disconnect from computer, then tap on the APK file, it will install the game.

Enjoy maadi.

Thanks
Maruthi