Only SQL 2008 SP1 is supported on Windows 2008 R2.
If you tried installing SQL 2008 from its DVD\ISO you surely got this error message:

In order to install SQL 2008 together with SP1, follow these Steps:
- Install the prerequisites of SQL 2008:
- .NET Framework 3.5 SP1 (from Server Manager --> Features --> .Net Framework 3.5.1 Features)
- Windows Installer 4.5
- Extract the service pack to a folder on the server using the following command:
- SQLServer2008SP1-KB968369-x64-ENU.exe /x:C:\SQL2008SP1
- Run the service pack to install the Setup files
- C:\SQL2008SP1\x64\setup\1033\sqlsupport.msi
- Run the Setup.exe file from the SQL 2008 source media by specifying the /PCUSource parameter:
- Setup.exe /PCUSource=C:\SQL2008SP1