All you have to do is donate $50 to my paypal and I will tell you... Na, lol.
Here it is:
Here’s how I installed my ATI Catlyst Driver 10.3 for the 5870 on Windows 7 x64, when the installer kept crashing.
1. Run the install package as per normal and wait for it to crash out.
2. Open a command prompy (Start / Run / CMD )
3. Type “CD C:\ATI\Support\10-3_vista64_win7_64_dd_ccc_wdm_enu/Bin64” and press enter
4. Type “ATISetup.exe -install -output screen” and press enter
Hope that work for you too.
Credit to D34N0 & Ozzie_O.