Hi Shrey,
I understand that you are unable to install Grid 2008 on your Windows 8 computer.
You can follow the link mentioned below to check the compatibility of the game with Windows 8.
http://www.microsoft.com/en-us/windows/compatibility/win8/CompatCenter/ProductDetailsViewer?Name=Grid&vendor=Codemasters&Locale=1033&ModelOrVersion=1&BreadCrumbPath=GRID%20&Type=Software&tempOsid=win8
I suggest you to place the computer in clean boot and then try to install the game in compatibility mode and check if it helps.
Method 1:
I suggest you to run the fixit mentioned below and check if it helps.
Fix problems with programs that can't be installed or uninstalled
http://support.microsoft.com/mats/program_install_and_uninstall/?wa=wsignin1.0
Method 2:
Perform Clean Boot to check if there are any conflicting programs, preventing the installation of the game.
To help troubleshoot error messages and other issues, you can start Windows by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts. Here is the link for your reference
to perform clean boot.
http://support.microsoft.com/kb/929135
Note: Please go through the section: How to reset the computer to start as usual after troubleshooting with clean boot of the KB article to boot the computer in normal startup
after fixing the issue.
Method 3:
If the issue still persists, I suggest you to you to install the game in compatibility mode and check if it helps.
What is program compatibility?
http://windows.microsoft.com/en-US/windows-8/what-program-compatibility
Make older programs compatible with this version of Windows
http://windows.microsoft.com/en-US/windows-8/older-programs-compatible-version-windows
Hope it resolves the issue.
If the issue persists or if you face any Windows issues in future, let us know and we would be glad to assist you.